21. You _____ me waiting for two hours. I _____ for you since five.

A. kept，waited 　　　　　　　　　　　　B. have kept，waited

C. kept，have waited 　　　　　　　　　　D. have kept，have waited

22. You can eat food free in my restaurant ________ you like.

A. wherever B. whatever C. whenever D. however

23. While watching TV，________.

A. the doorbell rang B. we heard the doorbell ring

C. the doorbell rings D. we heard the doorbell rings

24._______ the work，they have to stay there for another two weeks.

A. Not completing B. Not completed C. Not having completed D. Having not completed

25.She went to the bookstore and bought ________.

A. dozen books B. dozens books C. dozen of books D. dozens of books

26._______ I know the money is safe，I shall not worry about it.

A. As long as B. Unless C. Even though D. While

27. ——It's been a wonderful evening. Thank you very much.

—— _________.

A. I'm glad to hear that B. My pleasure C. No， thanks D. It’s OK

28. There is no light in the living room. They must have gone to the lecture，______?

A. didn't they B. haven't they C. don't they D. mustn't they

29. Stand over there _______ you'll be able to see it better.

A. or B. while C. but D. and

30. I failed in the final examination last term and only then ________ the importance of studies.

A. did I realize B. I realized C. I had realized D. had I realized