Ⅱ、单项选择（共15小题；每小题１分，计15分）
从下列各题A、B、C、D四个选项中选择一个能填入题干空白处的最佳答案。
( C)21. ---__ __number of cars on the roads is growing very fast.
---Yes. Therefore, __ ____number of problems have appeared.
A. A: a B. The; the C. A; the D. The; a
( C)22. Not only the students but also the teacher enjoying the film at that moment
A. are B. is C. were D. was
( C)23. The water in the river smells terrible, people must dirty things into it.
A. be stopped to throw B. be stopped from throwing
C. stop to throw D. stop from throwing
