28. had

29. will stay

30. swim

31. tell (unless = if)

32. don't change

33. wouldn't have bought

34. hang

35. would be

36. would have brought

37. would have been

38. wouldn't have printed

39. wouldn't buy

40. will arrive

3.

1. Unless you study harder, you'll get bad marks.

2. If this man isn't a driver, he can't help you move the car.

3. Unless he practices writing every day, he can't improvehis writing skill.

4. If you don't return this book to the library today, you'll have to pay a fine.

5. If you don't go out more often, you might fall ill.

6. Unless you aren't absent from school, you have to write a sick-note.

7. If the seas isn't warmmer, the ice at the North and South pole will not melt.

4. 

1. If they weren't absent now, they would meet the head master.

2. If he didn't clean up the car now, his boss could ask him to do this.

3. Unless I knew the number, I would not ring her up.

4. Unless Peter studied hard, he could not get good marks.

5. If he didn't refuse everything, he would lose his family.

6. If I didn't save my money, someone would take it.

5.

1. If you didn't try your best, you can't run fast .

2. If Tom weren't out, you would see him at home.

3. If the weather weren't nice, the boy wouldn't go swimming.

4. If everything hadn't been tidy, I would have felt pleasant.

5. If the noise hadn't been turned off, we could have slept well 

6. If people didn't hear you comming to my office, they wouldn't phone me.

7.  If you didn't live in the dormitory, you could annoy me.

8. If Ngoc hadn't been busy meeting his customers, she would have saved my kids from hot water.

9. If the student doesn't go to school early, he will be punished.

10. If Minh didn't love working on computers, he would get rid of his job.