21. Scientists say it may be five or six years _________　it is possible to test this medicine on human patients. ( 04 福建 ) 　A. since 　　　　　　　　　 B. after　　　　　　　　 C. before　　　　　　　 D. when

20. _____________ I know the money is safe, I shall not worry about it.　 (03 北京 )

　 A. Even though　　　　 B. Unless　　　　　　　 C. While　　　　　　　 D. As long as

19. He made a mistake, but then he corrected the situation ____________ it got worse.　 (03 北京 )

　 A. until　　　　　　　　　　 B. when　　　　　　　　 C. before　　　　　　　 D. as

18. - Was his father very strict with him when he was at school?

　 - Yes. He has never praised him ____________ he became one of the top students in his grade.　 (03 北京春季)

　 A. after　　　　　　　　　　 B. unless　　　　　　　 C. until　　　　　　　　 D. when

17. - Dad, I’ve finished my assignment.

-　　 Good, and ____________ you play or watch TV, you mustn’t disturb me.　 ( 03上海 )

A. whenever　　　　　　 B. whether　　　　　　 C. whatever　　　　　 D. no matter

16. Generally speaking, ____________ according to the directions, the drug has no side effect.　 ( 03上海 )

　 A. when taking　　　　　 B. when taken　　　　 C. when to take　　　 D. when to be taken

15. A good storyteller must be able to hold his listeners’ curiosity ____________ he reaches the end of the story.　 ( 03上海 )

　 A. when　　　　　　　　　　 B. unless　　　　　　　 C. after　　　　　　　　 D. until

14. - How far apart do they live?

-　　 _____________ I know, they live in the same neighbourhood.　 ( 03上海 )

A. As long as　　　　　　 B. As well as　　　　　 C. As far as　　　　　　 D. As often as

13. Americans eat _____________ vegetables per person today as they did in 1910. (02上海春季 )

　 A. more than twice　　　　　　　　　　　　　　　　 B. as twice as many

　 C. twice as many as　　　　　　　　　　　　　　　　 D. more than twice as many

12. - Did you remember to give Mary the money you owed her?

　 - Yes, I gave it to her ____________ I saw her.　 ( 01春季 )

　 A. while　　　　　　　　　 B. the moment　　　　　　　 C. suddenly　　　　　 D. once