31. While watching television, _______________________.

A. the doorbell rang 　　　　　　　　　　　　B. we heard the doorbell ring

C. there was someone knocking at the door　　 　D. we heard the doorbell rung

30. _______ by greater demand of vegetables, farmers have built more green houses.

A. Driven　　 　B. Being driven 　　　C. To drive 　　　D. Having driven

29. ________ they become dirty, the lakes are not able to clean themselves

A. Once　　　　 B. Since 　　　　C. As 　　　　D. Because

28. I think he is ________ to win, but I’m not sure.

A. possible 　　B. likely 　　　C. probably　　 　D. certain

27. The weather turned out to be fine yesterday, I ________ the trouble to carry my umbrella with me.

A. should have taken　　　　 B. could have taken

C. needn’t have taken　　　 　D. mustn’t have taken

26. They ______ a tent and got ready for the night when evening came.

A. put off　　 　　 B. put up　　　　 C. put on 　　　　 D. put out

25. –Did you go to the show last night?

–Yeah. Every boy and girl in the area _______ invited.

A. were　 B. have been　　　 C. has been　　　 D. was

24. –There is still a copy of the book in the library. Will you go and borrow ______?

–No, I’d rather buy ______ in the bookstore.

A. it; one　　　 B. one; one　　　 C. it; it　　　 D. one; it

23. John and I ________ friends for eight years. We first got to know each other at a Christmas party. But we _______ each other a couple of times before that.

A. had been; have seen　　　 B. have been; have seen

C. had been; had seen　 　　　D. have been; had seen

22. Swine flue is likely to cause _____ new round of panic all over ____ world.

A. a; a　　　　 B. the; the　　　 C. a; the　 　　D. the; a