Khi mở một lọ nước hoa, sau một thời gian rất ngắn, mùi thơm từ nước hoa lan ra khắp phòng. Đó là hiện tượng khuếch tán giữa các phân tử nước hoa và các phân tử không khí.

1. She will enjoy parties if she isn't shy.

2. If he takes more exercises, he will be healthy.

3. If I saw the signal, I would stop.

4. I will take you only if my father lends me a car.

5. If he saves enough money, he will buy a computer.

6. I will go with you tonight if I'm not busy.

7. If she was able to answer the questions, she wouldn't fail the exam.

8. If I had your phone number, I would call you.

9. If the sun didn't exist, we wouldn't.

10. If Peter wasn't nervous, he wouldn't fail the driving test.

11. If I have a watch, I will tell you what time it is.

12. If she learnt mathematics, she wouldn't be cheated by that salesman.

13. If the clock was right, we wouldn't miss the train.

14. She will by the dress if it isn't expensive.

15. The teacher wouldn't be angry if his pupils did their homework more carefully.