21. Students should be encouraged to use _____ Internet as ________ resource.
A. ／；a B. ／；the C. the；the D. the；a
【解析】选D。此题考查冠词。a resource 一种资源，泛指。根据句意“学生们被鼓励作为一种资源来利用因特网”。the Internet 因特网，特指。
22. So far this year we _______ a fall in house prices by between 5 and 10 percent.
A. saw B. see
C. had seen D. have seen
【解析】选D。so far到目前为止， 主句用现在完成时。根据句意“到目前为止，我们看到房价下降了5%到10%”。所以选D。
