31. I wrote to my parents once a week,____ I was too busy with my teaching work.

A. it　　　　 B. unless　　 C. when　　　　 D. as

30. However, at times this balance in nature is disturbed, ____ a number of possibly unforeseen effects.

A. lying in　　　 B. calling in　　 C. taking in　　　 D. resulting in

29.--- He has to finish the experiment today. He must be in the lab,____?

　　 ---That s quite possible.

A. mustn't he　　 B. won't he　　　 C. doesn't he　　 D. isn't he

28. Let us suppose that you are in____ position of____ parent. Would you allow your child to do such a thing?

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

27. Our TV sets sell well, but ten years ago no one could have imagined such a big share in the market that they ____.

A. were having　　　　　 B. had had　 　　　　　C. were to have　　　　 D. had

26. In salad bars the waiter does not bring you salad. You have to____ yourself, usually to as much as you want.

A. bring　　　 B. serve　　　 C. help　　 D. supply

25. ---How do you like the film?

　　 ---There was nothing special--- it was only ____.

A. average　　　 B. usual　　　　 C. normal　　　 D. common

24.--- What are you going to do next?

　　 --- To write a science story about outer space ___ by Science and Technology Press.

A. published　　 B. being published　　 C. to be published　　 D. publishing

23. I'll be home late, but please don't stay ____ for me.

A. up　　　　　　　　 B. in　　　　　　　　　 C. over　　　　　　　　 D. on

22. ---Mary has a very low opinion of George.

---It can' t be any worse than ____ of her.

A. he　　　　　　　　　 B. his　　　　　　　　　 C. him　　　　　　　　　 D. he does