17.It is at least ten years ________ these trees were planted.

A.　　 when B. before C. since D. as soon as

16.I was about to leave my house ________ the telephone rang.

A.　　 while B. as C. when D. since

15. ________ I came into the office, the teacher were having a meeting.

A.　　 While B. When C. Once D. Since

14.The boy didn’t stop talking ________ the second bell rang.

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

13.His brother has worked there ________ he left school.

A.　　 when B. after C. since D. until

12.The light went out while we ________ supper.

A. had　　　　　　　　　　　 B. had had

C. were having　　　　　　　 D. would have

11.________ he failed , he went on doing the experiment.

A. Even　　　 B. Yet　　　　 C. Although　　 D. in spite of

10.Write clearly ________ your teacher can understand you correctly.

A. since　　　 B. for　　　　 C. because　　 D. so that

9. You will not succeeded if you ________ harder.

A. will work　　　　　　　　 B. won’t work

C. work　　　　　　　 　　　　D. don’t work

8. English is ________ a useful language ________ it is spoken in many countries of the world.

A. so…that　　　　　　　　 B. such…that

C. so…because　　　　　　 D. such…because