16)She can speak quite fluent English. She____.
　　A)must been in the U.S.A. for some time
　　B)must have been in the U.S.A. for some time
　　C)should have been in the U.S.A. for some time
　　D)May be in the U.S.A. for some time

　　17)You should bear in mind that he is not so strong as he____.
　　A)was used to be
　　B)used to be
　　C)was used to
　　D)use to

　　18)“We didn't see him at the exhibition yesterday.”“He ___it.”
　　A)mustn't visit
　　B)can't have visited
　　C)should have gone to see
　　D)may see

　　19)Mary ____my letter,otherwise she would have replied before now.
　　A)should have received
　　B)has received
　　C)Couldn't have received
　　D)ought to have received

　　20)I ____ you a valuable present for your birthday,but I was short of money.
　　A)would have liked to give
　　B)liked to give
　　C)have liked to give
　　D)would like to give

　　答案：BBCCA