Here are the rewritten sentences:

1. The ferry couldn't sail due to the rough sea.
2. Since they went to HCM city, how long has it been?
3. I haven’t seen her since we left school.
4. She didn’t pass the exam because she was lazy.
5. He needs to solve this problem tomorrow.
6. His bike was stolen yesterday.
7. He delivered the sofa on Friday.
8. To whom does this car belong?
9. I have never eaten this kind of food before.
10. I apologize for not finishing my homework last night.
11. I wish you wouldn’t tell him.
12. The teachers have agreed to implement the new methods.
13. They found it unnecessary to call for help after all.
14. You don’t have to finish by Saturday.
15. The builder is scheduled to repair my roof tomorrow.
16. Please don’t touch this switch!
17. This switch shouldn’t be touched!
18. You shouldn’t drive so fast!
19. I would prefer if you didn’t drive so fast.
20. The play was so boring that he fell asleep.