21.　 You’d better come back earlier __A_____ it is getting colder.

A. as　 B. and　 C. but　 D. or

20.　 He always talks ___B____ he had been to outer space.

A. like　　 B. as if /though　　 C. because of　 D. as

19.　 Persist to the end , ____A___ you are the only one left.

A. even if /though　　 C. but　　 V. however　　 D. in spite of

18.　 We’ll carry the work through , cost __A_____ it may .

A. what　　 B. when　 C. where　 D. how

17.　 ___C____ you have got used to it , you’ll like it .

A. While　　 B. On the condition　　 C. Once　　 D. Unless

16.　 I paid only 5 pounds for the book , ___B____I expected it would cost.

A. not as many as　　 B. not so much as　 C. cheaper than　 D. not so expensive

15.　 __D_____I know , the computer can never take the place of the human brain.

A. As for　　 B. As long as　　 C. So far for　　 D. So /As far as

14.　 ____B___ did it , I didn’t.

A. Who　　 B. Whoever　　 C. No matter whom　　 D. No matter when　

13.　 I sent the letter early that morning ___B____ she got it that afternoon.

　 A. in order that　　 B. so that　　 C. for purpose that　 D. in order for

12.　 He wouldn’t give up smoking __C_____ his doctor told him it was a matter of life and death.

A. except　　 B. after　 C. until　　 D. in case