11. The reason _____ I can‘t come is that I have to prepare for the coming exam.

A. for B. as

C. because D. why

12. She studied hard at school when she was young； _____ contributes to her success in her career.

A. that B. so that

C. so D. which

13. Sound waves travel in the air in much the same way _____ water waves spread on the water.

A. as B. that

C. where D. in which

14. I‘ve got a bottle of beer， but I haven’t got anything _____ I can open it with.

A. that B. what

C. where D. which

15. Writers can accurately describe objects ______ have never seen.

A. who B. if they C. they D. that

16. It wasn‘t such a good present _____ he had promised me.

A. that B. as

C. which D. what

17. Perhaps the day will come _____ people will be able to breathe clean air in cities.

A. when B. while

C. as D. since

18. To make up an objective test， the teacher writes a series of questions， _____ has only one correct answer.

A. each of which B. some of which

C. which D. what

19. A higher crime rate exists in cities _____ a large percentage of unemployment.

A. where have B. that have

C. which they have D. that having

20. Scientists call Newton‘s idea _____ gravitation reaches throughout the universe the law of universal gravitation.

A. when B. which

C. that D. where