12、Only when he had handed in his exam paper, ____ he had made several grammatical mistakes.(B)

　　A、he realized

　　B、did he realize

　　C、he has realized

　　D、realized he

　　13、Hard ____ diamond is, it is quite easy to drill a hole in it with laser.(D)

　　A、although

　　B、though

　　C、like

　　D、as

　　14、No sooner ____ the bell rung than the class began.(A)

　　A、had

　　B、was

　　C、has

　　D、there was

　　15、____ had I sat down when I heard someone knocking at the door.(B)

　　A、No sooner

　　B、Hardly

　　C、Before

　　D、After

　　16、No teacher and no student ____ admitted into the laboratory.(D)

　　A、are

　　B、were

　　C、not is

　　D、is

　　17、Tom as well as two of his classmates ____ invited to the party last night.(D)

　　A、are

　　B、were

　　C、have

　　D、was

　　18、A committee of five men and three women ____ to consider the matter.(A)

　　A、is

　　B、are

　　C、were

　　D、will

　　19、During the holidays, every train and bus ____ crowded.(A)

　　A、was

　　B、are

　　C、were

　　D、are not

　　20、This is the key ____ an improvement of their living conditions.(B)

　　A、of

　　B、to

　　C、for

　　D、about

　　21、It is no use ____ him to come now. He is busy.( D)

　　A、ask

　　B、to ask

　　C、asked

　　D、asking

　　22、Fifteen miles ____ like a long walk to me.(C)

　　A、seem

　　B、is seemed

　　C、seems

　　D、are seemed

　　23、Other possibilities ____ at the meeting yesterday.(A)

　　A、were talked about

　　B、are talking about

　　C、is talked about

　　D、is talking about