1. Recycle and we'll save natural resources. 
If we recycle, we'll save natural resources.
2. Be careful or you will fall over the rocks
 If you don't be ceraful, you will fall over the rocks.
3. Working too much can make you feel tired.
If you workd too much, you will feel tired
4. Don't be careless or you'll break the vase
If you are careless, you’ll break the vase.
5. Ha can pass the exam, she has to work hard.
If Ha works hard, she can pass the exam.
6. He can do a part to save the environment by buying recycled products.
 If he buys recycled products, he can do a part to save the environment
7. Putting garbage into the bins is one answer to minimize pollution.
If we put garbage into the bins, we will minimize pollution.
8. We should take the map with us or we will lose our way on the street.
 If we don't take the map with us, we will lose our way on the street.
9. Ellen can borrow it, but she must give it back next week.
 If Ellen borrows it, she must give it back next week.
10. The authorities are thinking of raising the petrol prices. I will have to cycle to work.
If the authorities are thinking of raising the petrol prices, I will have to cycle to work.
b) Type 2:
1. I can't give you the answer because I don't know.
 If I knew the answer, I would give you.
2. Why don't you apply for the job?
 If I were you, I would apply for the job
3. I advise you to pay a visit to Nha Rong Harbor.
If I were you, I would pay a visit to Nha Rong Harbor.

4. But for his pension, he would starve.
 If he didn't have pension, he would starve.
5. How about going to school by bus?
If I were you, I would go to school by bus.
6. Mrs. Green has no money so he won't travel to the world.
 If Mrs.Green had money, he would travel to the world.
7. Rachel might fall her driving test. But she can take it again.
If Rachel fails her driving test, she can take it again.
8. The office might be closed. In that case Minh won't be able to walk in.
 If the office is closed, Minh won't be able to get in
9. You haven't got a pen, so you can't write down the address.
If you had got a pen, you could write down the address.
10. The number on those houses in this apartment aren't clearly numbered, therefore I find it difficult to find my cousin's house.
If the number on those houses in this apartment were clearly numbered, I wouldn't find it difficult to find my cousin’s house.
c) Type 3:
1. Jerry didn't understand the lesson. He didn't answer.
If Jerry has understood the lesson, he would have answered it.
2. Carol didn't answer the telephone because she was studying.
If Carol hadn't been studying, she would have answered the telephone.
3. Because he didn't study hard enough, he failed in the exam.
 If he had studied hard enought, he wouldn't have failed in the exam.
4. I was stuck in the traffic jam; and that's why I came late.
 If I hadn't been stuck in the traffic jam, I wouldn't have come late.
5. He had the flu because he went out in the rain last night.
If he hadn't gone out in the rain last night, he wouldn't have had the flu.
6. John didn't find the money. He didn't return it.
If John had found the money, he would have returned it.
7. I didn't know you were there. I didn't call you.
If I had known you were there, I would have called you
8. The heavy rain prevented everybody from going out.
If I had known you were there, I would have called you
9. Jimmy lent me the money. Otherwise, I would have gone out with business.
If Jimmy hadn't lent me the money, I would have gone out with business.
10. Without your help, I wouldn't  have succeeded this project.
If it hadn't been for your help, I wouldn’t have succeeded this project.
d) Mixed practice
1. Why don't study hard?

If you studied hard, you would pass the exams
2. Keep silent or you'll wake the baby up.
If you dont keep silent,you'll wake the baby up.
3. I don't know the answer, so I can't tell you. 
if I knew the answer, I could tell you
4. We got lost because we didn't have the map.
if we had had the map, we wouldn't have got lost
5. My friend was so late, so he missed the train.
if my friend hadn't been so late, he wouldn't have missed the train
6. This car is too heavy for me to move.
if this car was not heavy, I could move
7. Morning exercises make me feel healthy.
…if I didn't do morning exercises, I wouldn't feel healthy…

8. The church bells keep me from sleeping.
If the church bells didn't ring, I would keep on sleeping.
9. Without air, we would die. 
If there wasn't air, we would die
10. I advise him to stop smoking.
if he doesn't stop smoking, he will be unhealthy
11. Be calm, or you'll make a wrong decision.
Be calm, or you’ll make a wrong decision
12. Without a visa, he couldn't have come to that new country.
If he hadn't had a visa, he couldn't have come to that country
13. Today isn't Sunday, so the students don't go swimming.
if today were Sunday, the students would go swimming
14. Because you don't leave immediately, I call the policeman.
If you left immediately, I wouldn't call the policeman
15. I don't know her number, so I don't ring her up.
If I knew her number, I would ring her up
16. Go right now or you will be lte for the train.
If you go left now you will be late for the train.
17. As she is often absent from class, she can't keep pace with her classmates.
If she doesn't often absent from class ,she will keep pace with her classmate.
18. I couldn't write to Alice because I didn't know her address.
 If I know her dress, I could write to Alice.
19. The heavy rain kept everybody from going outdoors.
 If it hadn't rained heavily, everybody would have gone out

20. I didn't watch TV last night because I was busy.

If I hadn't been busy, I would have watched T.V last night.

21. People don't see the UFO, so they don't call the National UFO Reporting Center.
If people saw the UFO, they would call the National UFO Reporting Centre
22. Thu can't swim, so she doesn't go swimming in Lam Son Swimming pool. 
If Thu could swim,she would go swimming in Lam Son Swimming pool.
23. His flight was delayed so he couldn't be there on time.
If he had been there on time,his flight wouldn't have been delayed.
24. Thanks to Lisa's report, I was able to finish the project.
If Lisa hadn't reported me,I wouldn't have been able to finish the project.
25. Without your help, I couldn't overcome the problem.
If you hadn't helped me,I wouldn't have overcome this problem.

1. If we recycle, we'll save natural resources.

2. If you don't be ceraful, you will fall over the rocks.

3. If you workd too much, you will feel tired.

4. If you are careless, you’ll break the vase.

5. If Ha works hard, she can pass the exam.

6. If he buys recycled products, he can do a part to save the environment

7. If we put garbage into the bins, we will minimize pollution.

8. If we don't take the map with us, we will lose our way on the street.

9. If Ellen borrows it, she must give it back next week.

10. If the authorities are thinking of raising the petrol prices, I will have to cycle to work.