21. In the botanical garden we can find a(n) _______ of plants that range from tall trees to small flowers.

A. species       B. groups           C. amount            D. variety

22. This is a very special flower and it can _______ a strong sweet perfume at night.

A. give in        B. give up          C. give out            D. give out

23. If you _______ a mistake in reviewing the report, please bring it to my attention.

A. come along     B. come across      C. come around to     D. come about

24. In dealing with public relations, we should make every effort to prevent the _______ in personality.

A. contact          B. contrast         C. connection         D. conflict

25. It was __________ back home after he finished the report.

A. not until midnight did he go           B. until midnight that he didn’t go

C. not until midnight that he went         D. until midnight when he didn’t went

26. They are so close friends and their friendship ________ college days.

A. dates back to     B. dates back          C. dates to         D. dates back from

27. — Can you give me some advice about the design?

— I think it should _______ to all ages and social groups.

A. appear          B. appeal              C. suit             D. fit

28. The government not only ________ the refugees（难民）houses to live in, but also _______ them with food and clothes.

A. offered; offered      B. provided; provided     C. provided; offered    D. offered; provided