5. C
6. B
7. A
8. B
9. C
10. B
11. A
12. C
13. B
14. B
15. A
16. B
17. A
18. B
19. C
20. A
22. A
23. C
24. A
21. B
22. C
23. B
24. C
25. A
26. If we pollute the air, we will have breathing problems.
27. Although Mr. Peter is very old, he can run 3 kilometers.
28. Nga isn't as tall as Lan.
29. I has learnt/ learned English for 4 years.
30. I have ever been to Singapore.