20. Over the past decades, sea ice 　　　　in the Arctic as a result of global warming.

A. had decreased　　　 B. decreased　　 C. has been decreasing　 D. is decreasing

19. Life is like a long race　　　　 we compete with others to go beyond ourselves.

A. why　　 B. what　　 C. that　　　 D. where

18. I like　　　 in the autumn when the weather is clear and bright.

　 A. this　　　 B. that　　　 C. it　　　 D. one

17. It was the long March Rocket 2F, as reported, 　　　sent Shenzhou VI spaceship into space.

　 A. which　　 B. what　　 C. that　　　 D. as

16. Don’t leave the water　　　 while you brush your teeth.

　 A. run　　　 B .running　　 C. being run　 D. to run

15. -May I tell this to my close friend?

-No, you　　　 . Never let anybody else know about it.

　 A. needn’t　　　 B. shouldn’t　　　 C. mustn’t　　　　 D. can’t

14. The world is changing fast. I strongly believe that one will easily fall behind 　　　　he keeps on learning.

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

13. His speech at the meeting was really wonderful, and it could never be any　　　　 .

A. best　　　　　 B. better　　　　 C. worse　　 D. worst

12. All the　　　　　 indicate that he has been deeply involved in the crime.

A. evidence　　 B. fact　　 C. factors　　 D. cause

11. -Are you free after school?

-Sorry: I’ve planned to treat a friend of mine to dinner 　　　　for his help.

A. in terms　　　 B. in honor　　 C. in turn　　 D. in return