Sequence of Tenses

Rules Regarding Sequence of Tenses with Examples

Learning and understanding the rules for using multiple verbs in a sentence is essential to comprehend the sequence of tenses. Associating examples with these rules is crucial for mastering them. Below are the rules to follow when using multiple tenses:

Rule 1: Past Follows Past

If the main clause has a verb conjugated in the past tense, ensure that the subordinate clause also uses the past tense. This rule can be nuanced based on the form of past tense in the principal clause.

Tense of the Principal Clause	Tense of the Subordinate Clause	Example
Simple Past	Simple Past	I thought you were at home.
Past Continuous	Simple Past	They were telling us that they loved our performance.
Past Perfect	Simple Past	My parents had left home before I arrived.
Simple Past	Past Perfect	The teacher wanted to know if the students had completed writing the answers. When I reached the station, the train had already left.
Simple Past	Past Perfect Continuous	My brother was angry because he had been waiting for us for over an hour.

Exceptions to Rule 1:

1. Present Follows Past:

• In cases where the subordinate clause conveys a general fact, routine action, or universal truth, use the present tense even if the principal clause has a past tense verb.

• Example: The teacher taught us today that the Earth revolves around the Sun.

1. Any Tense in the Subordinate Clause:

• When making a comparison using 'than,' there is no specific rule for choosing the tense.

• Example: I would prefer going shopping with you rather than sitting at home all day doing nothing.

Rule 2: Any Tense after Present or Future Tense

If the principal clause is in the present or future tense, the subordinate clause can take any tense based on the conveyed information.

Tense of Principal Clause	Example
Present	He says he sees Krishna.
Future	My mom will be happy if you come home.
	She thinks that the food here is good.

Rule 3: Present Follows Future

When using subordinating conjunctions like 'when,' 'as soon as,' 'after,' etc., the subordinate clause takes the present tense when the verb in the principal clause is in the future tense.

Example

I will teach you after I finish learning.

Aruna will help her mom once she completes her assignments.

More Examples

1. I'll join the team after I finish my training. (NOT I'll join the team after I will finish my training.)

2. She promises to call before she leaves. (NOT She promises to call before she will leave.)

3. If you put in the effort, you'll excel. (NOT If you will put in the effort, you'll excel.)

The Present Perfect Tense in Subordinate Clauses

The present perfect tense is frequently used in subordinate clauses to denote future events. Remember, this construction is applicable only when the main clause verb is in the present or future tense.

1. We won't start the project until they have reviewed our proposal. (NOT We won't start the project until they will have reviewed our proposal.)

2. After I've had my meeting, we can discuss your ideas. (NOT After I will have had my meeting, we can discuss your ideas.)

Rule 4: Use of Past Tense in Subordinate Clauses

When using phrases like 'as if,' 'it is time/high time,' 'what if,' 'wish that,' etc., use the past tense form of the verb.

Example

I wish I had known you earlier.

She acted as if none of this affected her.

It is high time you consulted a doctor.

Rule 5: Use of Modal Verbs When the Conjunction 'That' Is Used

If a subordinate clause starts with the conjunction 'that' or 'so that,' use 'may' for present tense in the principal clause and 'might' for past tense.

Example

We work hard so that we may prosper.

They worked hard so that they might not perish.

Complete the sentences with the appropriate verb form from the given brackets.

1. The children insisted that they _______ to the zoo. (go)

2. Even though they _______ late, they managed to catch the last train. (arrive)

3. She acted as if she _______ that fact before. (know – negative)

4. I wish you _______ me sooner. (meet)

5. When he arrived, they realized he _______ them a surprise. (prepare)

6. You will be amazed when you find out how much he _______ for the project. (sacrifice)

7. It's crucial that you _______ your point clearly. (express)

8. Unless we _______ for the event in advance, we _______ good seats. (plan, not get)

9. The scientist explained that the Earth _______ around the sun. (revolve)

10. She believes that it _______ the right decision. (be)

Answers:

1. The children insisted that they go to the zoo.

2. Even though they arrived late, they managed to catch the last train.

3. She acted as if she did not know that fact before.

4. I wish you had met me sooner.

5. When he arrived, they realized he had prepared them a surprise.

6. You will be amazed when you find out how much he has sacrificed for the project.

7. It's crucial that you express your point clearly.

8. Unless we plan for the event in advance, we will not get good seats.

9. The scientist explained that the Earth revolves around the sun.

10. She believes that it was the right decision.

Fill in the blanks with the correct form of the verb given in brackets:

1. She insisted that she __________ (complete) the assignment before the deadline.

2. After they __________ (finish) their meal, they went for a walk.

3. If he __________ (study) harder, he __________ (pass) the exam.

4. By the time I __________ (arrive), they __________ (already/start) the meeting.

5. The teacher explained that water __________ (boil) at 100 degrees Celsius.

6. I will call you as soon as I __________ (reach) the airport.

7. They __________ (not/realize) that the concert __________ (already/start) when they arrived.

8. She wishes she __________ (learn) Spanish when she was younger.

9. We __________ (not/leave) until the rain __________ (stop).

10. If they __________ (invite) us, we __________ (attend) the party.

11. The manager told us that the new project __________ (begin) next month.

12. By the time you __________ (read) this, I __________ (already/leave).

13. I'll believe it when I __________ (see) it.

14. She __________ (not/hear) the news until her friend __________ (tell) her.

15. If you __________ (exercise) regularly, you __________ (feel) better.

16. The company announced that they __________ (launch) a new product next year.

17. After the storm __________ (pass), we __________ (inspect) the damage.

18. He __________ (not/realize) that he __________ (lose) his wallet until he got home.

19. I __________ (wish) I __________ (know) about the traffic before leaving.

20. We __________ (not/start) the movie until everyone __________ (arrive).

answers:

1. has completed

2. finished

3. studies, will pass

4. arrive, had already started

5. boils

6. reach

7. did not realize, had already started

8. had learned

9. will not leave, stops

10. invite, will attend

11. will begin

12. read, will have already left

13. see

14. had not heard, told

15. exercise, will feel

16. will launch

17. passes, will inspect

18. did not realize, had lost

19. wish, had known

20. will not start, arrives

Fill in the blanks with the correct form of the verb given in brackets:

1. By the time he __________ (arrive) at the conference, most of the attendees __________ (already/leave).

2. If she __________ (know) about the deadline, she __________ (submit) the report earlier.

3. The author explained that he __________ (work) on the novel for several years before he __________ (finally/publish) it.

4. They __________ (not/realize) that the prices __________ (already/rise) when they __________ (decide) to invest.

5. After the negotiations __________ (conclude), the representatives __________ (exchange) pleasantries.

6. If the weather __________ (be) good tomorrow, we __________ (have) a picnic.

7. She __________ (study) Italian for years before she __________ (visit) Italy.

8. The team __________ (train) hard because they __________ (compete) in the championship next month.

9. By the time you __________ (read) this book, the author __________ (already/write) another one.

10. He __________ (promise) that he __________ (help) us, but he __________ (not/keep) his word.

answers:

1. arrived, had already left

2. had known, would have submitted

3. had worked, finally published

4. did not realize, had already risen, decided

5. concluded, exchanged

6. is, will have

7. had studied, visited

8. is training, will compete

9. read, will have already written

10. promised, would help, did not keep

Fill in the blanks with the correct form of the verb given in brackets:

1. The scientists __________ (conduct) research on this topic for years before they __________ (publish) their findings.

2. If you __________ (study) harder, you __________ (perform) better in exams.

3. By the time they __________ (reach) the summit, the sun __________ (already/set).

4. She __________ (work) on the project until she __________ (realize) it __________ (be) not feasible.

5. After he __________ (win) the championship, he __________ (announce) his retirement.

6. The CEO __________ (state) that the company __________ (not/tolerate) any unethical behavior.

7. When the guests __________ (arrive), dinner __________ (already/serve).

8. I __________ (understand) the concept after my teacher __________ (explain) it several times.

9. If she __________ (know) about the traffic, she __________ (not/be) late for the meeting.

10. By the time we __________ (complete) the project, the client __________ (change) the requirements.

11. He __________ (train) rigorously because he __________ (compete) in the marathon next month.

12. After she __________ (graduate), she __________ (start) her own business.

13. They __________ (not/anticipate) that the market __________ (experience) a sudden downturn.

14. The artist __________ (paint) many masterpieces before he __________ (gain) recognition.

15. If the weather __________ (be) good, we __________ (visit) the botanical garden.

16. By the time you __________ (read) this, I __________ (already/leave) for my vacation.

17. I __________ (wish) I __________ (know) how to play the guitar when I was younger.

18. The detective __________ (solve) the case before he __________ (reveal) the culprit.

19. After he __________ (find) a job, he __________ (decide) to pursue further studies.

20. The team __________ (celebrate) their victory as soon as the match __________ (end).

21. If we __________ (not/act) quickly, the situation __________ (get) out of control.

22. The professor __________ (advise) that we __________ (focus) on the fundamental concepts first.

23. She __________ (not/know) that the concert __________ (cancel) until she __________ (arrive) at the venue.

24. Once the movie __________ (begin), no one __________ (be) allowed to enter the cinema.

25. The chef __________ (prepare) a delicious meal after he __________ (receive) the fresh ingredients.

26. They __________ (wait) for hours before they __________ (realize) the bus __________ (break) down.

27. After the storm __________ (pass), the residents __________ (assess) the damage.

28. I __________ (promise) that I __________ (help) you, and I __________ (intend) to keep my promise.

29. By the time you __________ (arrive), the party __________ (already/start).

30. If he __________ (attend) the workshop, he __________ (learn) valuable skills.

Answers:

1. had conducted, published

2. studied, would perform

3. reached, had already set

4. worked, realized, was

5. won, announced

6. stated, would not tolerate

7. arrived, had already been served

8. understood, explained

9. had known, would not have been

10. complete, had changed

11. trained, will compete

12. graduated, started

13. did not anticipate, experienced

14. painted, gained

15. is, will visit

16. read, will have already left

17. wish, had known

18. solved, revealed

19. found, decided

20. celebrated, ended

21. do not act, will get

22. advised, should focus

23. did not know, was canceled, arrived

24. begins, will be

25. prepared, received

26. waited, realized, had broken

27. passes, will assess

28. promised, will help, intend

29. arrive, will have already started

30. attends, will learn

Fill in the blanks with the correct form of the verb given in brackets:

1. After she __________ (finish) her degree, she __________ (consider) pursuing a master's.

2. He __________ (travel) extensively before he __________ (decide) to settle down.

3. If they __________ (invest) wisely, they __________ (gain) substantial returns.

4. By the time I __________ (arrive), the party __________ (already/start).

5. The students __________ (not/realize) that the exam __________ (already/begin) when they __________ (enter) the room.

6. I __________ (wish) I __________ (know) about the sale before everything __________ (sell) out.

7. Once he __________ (complete) the training program, he __________ (apply) for the job.

8. If you __________ (ask) me earlier, I __________ (help) you with the project.

9. After the storm __________ (pass), the crew __________ (start) repairing the damaged roof.

10. She __________ (promise) that she __________ (visit) us, but she __________ (not/keep) her promise.

11. They __________ (not/expect) that the prices __________ (rise) when they __________ (make) the investment.

12. By the time we __________ (reach) the theater, the movie __________ (already/begin).

13. We __________ (not/realize) that he __________ (already/leave) until we __________ (arrive).

14. I __________ (tell) you everything after I __________ (receive) more information.

15. If you __________ (learn) the rules, you __________ (avoid) making mistakes.

16. The artist __________ (work) tirelessly until he __________ (create) a masterpiece.

17. Once she __________ (finish) the report, she __________ (submit) it to the supervisor.

18. The manager __________ (state) that the company __________ (not/tolerate) any form of discrimination.

19. If they __________ (start) the project earlier, they __________ (finish) it on time.

20. He __________ (apologize) for the mistake after he __________ (realize) what happened.

21. They __________ (wait) for hours before the doctor __________ (arrive).

22. After the concert __________ (conclude), the musicians __________ (greet) the audience.

23. She __________ (wish) she __________ (attend) the conference when she __________ (have) the chance.

24. Once the results __________ (be) announced, the winners __________ (celebrate) their success.

25. He __________ (not/understand) that he __________ (make) a wrong turn until he __________ (drive) for miles.

26. The teacher __________ (recommend) that they __________ (read) the book before the discussion.

27. After the guests __________ (leave), we __________ (clean) up the party venue.

28. If they __________ (start) exercising regularly, they __________ (notice) improvements in their health.

29. The team __________ (not/realize) that they __________ (qualify) for the finals until the coach __________ (inform) them.

30. I __________ (have) lunch after I __________ (complete) this task.

31. He __________ (feel) regret after he __________ (realize) his mistake.

32. She __________ (apologize) for the delay once she __________ (arrive).

33. If she __________ (study) harder, she __________ (excel) in her exams.

34. They __________ (wish) they __________ (know) about the event before it __________ (occur).

35. Once the committee __________ (reach) a decision, they __________ (announce) it to the public.

36. If we __________ (not/act) promptly, the situation __________ (escalate).

37. She __________ (not/expect) that the seminar __________ (be) so informative when she __________ (register).

38. After the movie __________ (end), the audience __________ (applaud) the actors.

39. He __________ (regret) not taking the opportunity after he __________ (learn) about its benefits.

40. Once they __________ (arrive), we __________ (begin) the meeting.

Answers:

1. finishes, will consider

2. traveled, decided

3. invest, will gain

4. arrive, will have already started

5. did not realize, had already begun, entered

6. wish, had known, sold

7. completes, will apply

8. had asked, would have helped

9. passes, will start

10. promised, would visit, did not keep

11. did not expect, had risen, made

12. reach, will have already begun

13. did not realize, had already left, arrived

14. will tell, receive

15. learn, will avoid

16. worked, created

17. finishes, will submit

18. stated, will not tolerate

19. had started, would have finished

20. will apologize, realizes

21. waited, will arrive

22. concludes, will greet

23. wishes, had attended, had the chance

24. are, will celebrate

25. did not understand, had made, drove

26. recommended, read

27. leave, will clean

28. start, will notice

29. did not realize, had qualified, informed

30. will have, complete

31. felt, realized

32. apologized, arrived

33. studied, would excel

34. wish, had known, occurred

35. reaches, will announce

36. do not act, will escalate

37. did not expect, was, registered

38. ends, will applaud

39. regrets, learned

40. arrive, will begin

Correction:

1. Incorrect: She wished she can visit the museum when she was in Paris. Correct: She wished she could visit the museum when she was in Paris. Explanation: In reported speech or expressions of wish, use the past tense form ("could") to maintain the sequence of tenses.

2. Incorrect: If he knows about the plan, he would participate. Correct: If he knew about the plan, he would participate. Explanation: Use the past tense ("knew") after "if" to maintain the correct sequence.

3. Incorrect: After she will finish her work, she will join us for dinner. Correct: After she finishes her work, she will join us for dinner. Explanation: Avoid using "will" after "after." The base form of the verb is used.

4. Incorrect: We won't leave until he will arrive. Correct: We won't leave until he arrives. Explanation: Avoid using "will" after "until." The base form of the verb is used in the subordinate clause.

5. Incorrect: Once they will understand the concept, it will be easier. Correct: Once they understand the concept, it will be easier. Explanation: Avoid using "will" after "once." The base form of the verb is used.

6. Incorrect: By the time he will reach the station, the train will leave. Correct: By the time he reaches the station, the train will leave. Explanation: Use the base form of the verb ("reaches") after "by the time" to maintain the correct sequence.

7. Incorrect: The company announced that they will launch a new product last month. Correct: The company announced that they would launch a new product last month. Explanation: In reported speech or in clauses introduced by verbs like "announce," we use "would" instead of "will" to maintain the sequence of tenses.

8. Incorrect: She apologized once she will realize her mistake. Correct: She apologized once she realized her mistake. Explanation: Avoid using "will" after "once." The base form of the verb is used.

9. Incorrect: If she studies harder, she would have excelled in her exams. Correct: If she had studied harder, she would have excelled in her exams. Explanation: Use the past perfect tense ("had studied") to maintain the correct sequence.

10. Incorrect: After the storm passes, they will start cleaning up the debris. Correct: After the storm passes, they will start cleaning up the debris. Explanation: The original sentence is correct. No error.

11. Incorrect: I wish I will have known about the event earlier. Correct: I wish I had known about the event earlier. Explanation: Use the past perfect tense ("had known") in expressions of wish to maintain the sequence of tenses.

12. Incorrect: When the guests arrived, the dinner already serves. Correct: When the guests arrived, the dinner had already been served. Explanation: Use the past perfect tense ("had already been served") to indicate an action completed before another past action.

13. Incorrect: I'll believe it when I will see it. Correct: I'll believe it when I see it. Explanation: Avoid using "will" after "when." The base form of the verb is used.

14. Incorrect: He insisted that he will pay for the expenses. Correct: He insisted that he would pay for the expenses. Explanation: In reported speech or in clauses introduced by verbs like "insist," we use "would" instead of "will" to maintain the sequence of tenses.

15. Incorrect: They won't leave until you will give them permission. Correct: They won't leave until you give them permission. Explanation: Avoid using "will" after "until." The base form of the verb is used in the subordinate clause.

16. Incorrect: Once the concert will conclude, the audience will leave. Correct: Once the concert concludes, the audience will leave. Explanation: Avoid using "will" after "once." The base form of the verb is used.

17. Incorrect: If they know the answer, they would raise their hands. Correct: If they knew the answer, they would raise their hands. Explanation: Use the past tense ("knew") after "if" to maintain the correct sequence.

18. Incorrect: We won't start the game until the coach will arrive. Correct: We won't start the game until the coach arrives. Explanation: Avoid using "will" after "until." The base form of the verb is used in the subordinate clause.

19. Incorrect: After the movie will end, we can discuss our thoughts. Correct: After the movie ends, we can discuss our thoughts. Explanation: Avoid using "will" after "after." The base form of the verb is used.

20. Incorrect: The students didn't realize the exam already begins when they entered the room. Correct: The students didn't realize the exam had already begun when they entered the room. Explanation: Use the past perfect tense ("had already begun") to express an action completed before another past action.

Identify and correct the errors in the given sentences:

1. She insisted that she will finish the project by tomorrow.

2. By the time they arrived, the meeting already started.

3. If he knew about the issue, he would solve it immediately.

4. We won't leave until you will arrive.

5. Once the concert will conclude, the audience will leave the hall.

6. After they will complete the training, they apply for the job.

7. He wished he knows how to play the piano.

8. When the guests arrived, the dinner already served.

9. I will call you as soon as I will reach home.

10. The students didn't realize the exam already began when they entered the room.

Corrected sentences:

1. She insisted that she would finish the project by tomorrow.

2. By the time they arrived, the meeting had already started.

3. If he knew about the issue, he would solve it immediately. (No error)

4. We won't leave until you arrive.

5. Once the concert concludes, the audience will leave the hall.

6. After they complete the training, they will apply for the job.

7. He wished he knew how to play the piano.

8. When the guests arrived, the dinner had already been served.

9. I will call you as soon as I reach home.

10. The students didn't realize the exam had already begun when they entered the room.

Explanations for the corrections:

1. Original: She insisted that she will finish the project by tomorrow. Correction: She insisted that she would finish the project by tomorrow. Explanation: In reported speech or in clauses introduced by verbs like "insist," we use "would" instead of "will" to maintain the sequence of tenses.

2. Original: By the time they arrived, the meeting already started. Correction: By the time they arrived, the meeting had already started. Explanation: When expressing an action that occurred before another past action, use the past perfect tense ("had already started") to maintain the sequence of tenses.

3. Original: If he knew about the issue, he would solve it immediately. Correction: If he knew about the issue, he would have solved it immediately. Explanation: When referring to a condition that is contrary to reality in the past, use the past perfect tense ("would have solved") to maintain the correct sequence.

4. Original: We won't leave until you will arrive. Correction: We won't leave until you arrive. Explanation: Avoid using "will" after "until." The base form of the verb is used in the subordinate clause.

5. Original: Once the concert will conclude, the audience will leave the hall. Correction: Once the concert concludes, the audience will leave the hall. Explanation: Use the base form of the verb ("concludes") after subordinating conjunctions like "once."

6. Original: After they will complete the training, they apply for the job. Correction: After they complete the training, they will apply for the job. Explanation: Use "will" before the verb in the future action to maintain the sequence.

7. Original: He wished he knows how to play the piano. Correction: He wished he knew how to play the piano. Explanation: In reported speech or expressions of wish, use the past tense form ("knew") to maintain the sequence of tenses.

8. Original: When the guests arrived, the dinner already served. Correction: When the guests arrived, the dinner had already been served. Explanation: Use the past perfect tense ("had already been served") to indicate an action completed before another past action.

9. Original: I will call you as soon as I will reach home. Correction: I will call you as soon as I reach home. Explanation: Avoid using "will" after conjunctions like "as soon as." The base form of the verb is used.

10. Original: The students didn't realize the exam already began when they entered the room. Correction: The students didn't realize the exam had already begun when they entered the room. Explanation: Use the past perfect tense ("had already begun") to express an action completed before another past action.

Identify and correct the errors in the given sentences:

1. After he finishes his work, he will join us for lunch.

2. We won't start the meeting until everyone will arrive.

3. If they knew about the plan, they would participate.

4. By the time she will return, we will finish the project.

5. The teacher explained that the Earth revolves around the Sun.

6. Once you will understand the concept, it will be easier.

7. After the storm passed, they started cleaning up the debris.

8. She wished she could visit the museum when she was in Paris.

9. I'll believe it when I will see it.

10. The company announced that they will launch a new product next year.

11. He insisted that he will pay for the dinner.

12. When the guests arrived, the dinner already served.

13. She apologized once she will realize her mistake.

14. If she studies harder, she would excel in her exams.

15. They won't leave until you will give them permission.

16. After the movie will end, we will discuss our thoughts.

17. I wish I know how to play the guitar when I was younger.

18. He promised that he will help us, but he never did.

19. The students didn't realize the exam already began when they entered the room.

20. Once they arrive, we will start the conference.

Corrected sentences:

1. After he finishes his work, he will join us for lunch.

2. We won't start the meeting until everyone arrives.

3. If they knew about the plan, they would participate. (No error)

4. By the time she returns, we will finish the project.

5. The teacher explained that the Earth revolves around the Sun. (No error)

6. Once you understand the concept, it will be easier.

7. After the storm passed, they started cleaning up the debris. (No error)

8. She wished she could visit the museum when she was in Paris. (No error)

9. I'll believe it when I see it.

10. The company announced that they will launch a new product next year. (No error)

11. He insisted that he would pay for the dinner.

12. When the guests arrived, the dinner had already been served.

13. She apologized once she realized her mistake.

14. If she studies harder, she will excel in her exams.

15. They won't leave until you give them permission. (No error)

16. After the movie ends, we will discuss our thoughts.

17. I wish I knew how to play the guitar when I was younger.

18. He promised that he would help us, but he never did. (No error)

19. The students didn't realize the exam had already begun when they entered the room.

20. Once they arrive, we will start the conference.

Explanation:

1. Original: After he finishes his work, he will join us for lunch. Correction: After he finishes his work, he will join us for lunch. Explanation: The original sentence is correct. No error.

2. Original: We won't start the meeting until everyone will arrive. Correction: We won't start the meeting until everyone arrives. Explanation: Avoid using "will" after "until." The base form of the verb is used in the subordinate clause.

3. Original: If they knew about the plan, they would participate. Correction: If they knew about the plan, they would participate. Explanation: The original sentence is correct. No error.

4. Original: By the time she will return, we will finish the project. Correction: By the time she returns, we will finish the project. Explanation: Use the base form of the verb ("returns") after "by the time" to maintain the correct sequence.

5. Original: The teacher explained that the Earth revolves around the Sun. Correction: The teacher explained that the Earth revolves around the Sun. Explanation: The original sentence is correct. No error.

6. Original: Once you will understand the concept, it will be easier. Correction: Once you understand the concept, it will be easier. Explanation: Avoid using "will" after "once." The base form of the verb is used.

7. Original: After the storm passed, they started cleaning up the debris. Correction: After the storm passed, they started cleaning up the debris. Explanation: The original sentence is correct. No error.

8. Original: She wished she could visit the museum when she was in Paris. Correction: She wished she could visit the museum when she was in Paris. Explanation: The original sentence is correct. No error.

9. Original: I'll believe it when I will see it. Correction: I'll believe it when I see it. Explanation: Avoid using "will" after "when." The base form of the verb is used.

10. Original: The company announced that they will launch a new product next year. Correction: The company announced that they will launch a new product next year. Explanation: The original sentence is correct. No error.

11. Original: He insisted that he will pay for the dinner. Correction: He insisted that he would pay for the dinner. Explanation: In reported speech or in clauses introduced by verbs like "insist," we use "would" instead of "will" to maintain the sequence of tenses.

12. Original: When the guests arrived, the dinner already served. Correction: When the guests arrived, the dinner had already been served. Explanation: Use the past perfect tense ("had already been served") to indicate an action completed before another past action.

13. Original: She apologized once she will realize her mistake. Correction: She apologized once she realized her mistake. Explanation: Avoid using "will" after "once." The base form of the verb is used.

14. Original: If she studies harder, she will excel in her exams. Correction: If she studies harder, she will excel in her exams. Explanation: The original sentence is correct. No error.

15. Original: They won't leave until you will give them permission. Correction: They won't leave until you give them permission. Explanation: Avoid using "will" after "until." The base form of the verb is used in the subordinate clause.

16. Original: After the movie will end, we will discuss our thoughts. Correction: After the movie ends, we will discuss our thoughts. Explanation: Avoid using "will" after "after." The base form of the verb is used.

17. Original: I wish I knew how to play the guitar when I was younger. Correction: I wish I knew how to play the guitar when I was younger. Explanation: The original sentence is correct. No error.

18. Original: He promised that he will help us, but he never did. Correction: He promised that he would help us, but he never did. Explanation: In reported speech or in clauses introduced by verbs like "promise," we use "would" instead of "will" to maintain the sequence of tenses.

19. Original: The students didn't realize the exam already began when they entered the room. Correction: The students didn't realize the exam had already begun when they entered the room. Explanation: Use the past perfect tense ("had already begun") to express an action completed before another past action.

20. Original: Once they arrive, we will start the conference. Correction: Once they arrive, we will start the conference. Explanation: The original sentence is correct. No error.