21. Jim says we ______ stay in his house as long as we leave it clean and tidy.

A. must        B. can       C. need      D. should     

22. Dr. Rowan, ________ secretary retired two weeks ago, has had to do all his own   typing.

A. whose          B. of whom        C. of which        D. which

23. The number of medical schools reached 18 in the early 1990s and _______ around that level ever since.

A. are remaining  B. have remained    C. is remaining    D. has remained 

24. --Why do people like pop music? I hate it so much.

--_______ it is not your style, that doesn’t mean it is bad.

A. Only if       B. Even though      C. Now that     D. In case