15. If he had revised all his lessons, he wouldn't have failed the exam.

16. But for his sister's money, he wouldn't have continued to study

17. If you walk for 5 minutes, you will see the park.

18. If it rains, we'll stay at home

19. If I were you, I would cut down on smoking right now

20. Unless you leave me alone, I'll call the police

IV 
1. If you don't keep silent, you'll wake the baby up

2. If you don't stop talking, you won't understand the lesson

3. If I know her number, I will ring her up

4. If I know the answer, I'll tell you

5. If we had had a map, we would have got lost

6. If Susan hadn't eaten 4 cream cakes, she wouldn't have felt sick

7. If it hadn't been for this treatment, the patient would have died

8. If he hadn't been late every day, he wouldn't have lost his job

9. If Peter didn't eat so many chips, he wouldn't be fat

10. If Robert hadn't smoked cigarettes, he wouldn't have got a bad cough

V

1. Unless you like this one, I'll bring you another

2. Unless she hurries, she'll be late

3. Unless you are careful, you'll cut yourself

4. Unless you had sneezed, he wouldn't have known that we were there