1-B
2-A
3-A
4-A
5-B
6-C
7-A
8-A
9-A
10-C
11-C
12-D
13-D
14-A
15-A

1-B
2-D
3-B
4-C
5-A
6-A

31. I've been looking for this book for a long time.

32. I've been working since I got up.

33. The kettle has been boiling for ten minutes

34. They have been living in Madrid since 1972.

35. He has been in prison for four years.

36. He has known about the fact for a long time.

37. Conditions have changed a lot since we were children.

38. Our teacher has been very ill since the last month.

39. I haven't eaten anything for twenty-four hours.

40. In fact he is always very rude. We have been waiting for him for half an hour.

41. I haven't seen him for three years. It is because I haven't been there since I left school.

42. I have been trying to mend this old fashioned car for hours.

43. One of my friends has been teaching in Tokyo for three years. I haven't met him since last year.

44. I haven't enjoyed myself for two weeks since I heard that my final exam grades were low.

45. I know that you have never seen a lion since you were born. Then now I say that we can go to the zoo and see one.

3,How often do they play soccer?
   They rarely play soccer.
4,How often does Mr.Hai plays soccer?
   He rarely plays soccer.
5,How often does his have barbecues?
   He never have barbecues.
6,How often do they have barbecues?
   They never have barbecues.

B,kích thước hạt to

9 x 3 : 864
=27 : 864
=0,03