(    ) 3. Many_____ trees should be planted on the mountains.

          A. thousand                           B. thousand of   

          C. thousands of                       D. thousands

(    ) 4. The boys who _____ football are all from the same country.

          A. are playing     B. is playing      C. plays      D. to play

(    ) 5. This is the most interesting film _____ I have ever seen.

         A. that            B. where           C. who        D. which

(    ) 6. One third of the population of China _____ workers.

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

(    ) 7. I found him very _____ after work.

          A. to tire         B. tiring          C. tire       D. tired