24. The boy as well as his sister ___________ the museum.

　　　 A. are visiting　　　　 B. is visiting　　　　　 C. visit　　　　　　　　　 D. have visited

23.　 ________________ the same answer, he solved the problem a third time.

　　　 A. Having not　　　　 B. Not had　　　　　　 C. Having not got　 D. Not having got

22.　 The young trees _______ thirty years ago have become thick woods.

　　　 A. being planted　　 B. planted　　　　　　　 C. having planted　 D. planting

21.　 They have done something to prevented the air ________________.

　　　 A. from polluting　 B. being polluting　 C. from being polluted　 D. to be polluted

20. He prefers _______ in the bookstore to watching TV at home.

　　　 A. to stay　　　　　　　　　　 B. stay　　　　　　　　　 C. staying　　　　　　　 D. to be stayed

19. China was one of the first countries in the world _________ the science of farming.

　　　 A. who was studied　　　　　　　 B. of study　　 C. studied　　　　　　　 D. to study

18. Could you give me a plastic bag _____________?

　　　 A. to put these things in　　　　　　　　　　　 B. to put these things

　　　 C. of putting things　　　　　　　　　　　　　　　　　 D. for putting things

17. This factory is ________ we visited with my friends last week.

　　　 A. which　　　　　　　 B. that　　　　　　　　　 C. on which　　　　　 D. the one

16.　 The date ________ he wrote down on the paper was wrong.

A. when　　　　　　　　 B. on that　　　　　　　　　　 C. which　　　　　　　 D. on which

15. Helen is always the first ____ to the office and the last _____.

A. of coming, of leaving　 B. comes, leaves　 C. to come, to leave　 D. coming, leaving