51. You must be fifty, ________?

　 A. mustn't you　　 B. needn't you　　　　　 C. aren't you　　　 D. mnyn't you

50. Since the ground is white, it _________ last night.

　 A. had snowed　　 B. must have snowed　 C. must be snowing　　 D. must have been snowing

49. They _________ the plane, or perhaps they have been prevented from coming for some reason.

　 A. can have missed　　 B. may have missed　　　　 C. can have lost　　　 D. may have lost

48. ------"We didn't see him at the lecture yesterday. "　　　　　　　 　　

　 ------"He _________ it. "

　 A. mustn't attend　 B. can't have attended　 C. would have not attended 　D. needed have attended

47. ---- _________ this book be yours?　　　　　　　

　 ---- No, it ________ not be mine. It ________ be his.

　 A. Can, must, may　　 B. May, might, must　　　　 C. Can, may, must 　D. Must, can, may

46. I went to the doctor's yesterday, I had to wait for half an hour before he ________ see me.

　 A. can　　 B. may　　 C. might　　 D. could

45.He was a good swimmer so he _________ swim to the river bank when the boat sank.

　 A. could　　 B. might　　 C. should　　 D. was able to

44.The bus _____start;I don’t know what to do with it.

　’t　 　　　　B.won’t　　 　　　　　C.shan’t　 　　　　　　　D.may not

43.--------Must I take a taxi?

　 -------No,you_____.You can walk from here.

　 A.don’t　 　　　　B.must not　 　　　　　C.don’t have to　 　　　　　D.had better not to

42.------Don’t forget to post the letter for me.

　 ------I _____.

　 A.won’t　 　　　　B.will　 　　　　　　C.don’t　　 　　　　　　’t