Bài a:

1. younger => youngest

2. busyer => busier

3. that => than

4. China => chinese

5. have => has

Bài b:

1. His house is to the right of the bookstore.

2. It's a tall building.

3. Tom travels to work by car every morning.

4.  ko rõ lắm nên chưa làm đc

9. weren't

10. was

11. where were you

12. Did they help

13. hasn't play

14. called

15. moved

16. have been

17.  went

18. spent

19. heard

20.  have you finished

21. will go

22. goes

23. will visit

24. collected

25. have you ever done

26. goes

27. go

28. seeing

29. to play

30. has learned

31. watched

32. arranging

33.  working

34. swimming

35. eating

36. living

37. watching

38. built

39. organized

40. visited

41. will you be