20. ______ from other continents for millions of years, Australia has many plants and animals that cannot be found anywhere else in the world.

　　　 A. Being separated　　　　　　　　　　　　　　　　　　 B. Having separated

　　　 C. Having been separated 　　　　　　　　　　　　 D. Separating

19. A modern city has been set up in _______ was a wasteland ten years ago.

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

18. There was a loud scream from the backstage immediately after the concert ended, ________?

　　　 A. wasn’t there　　　　　 B. was there　　　　　　　 C. didn’t it　　　　　　　　 D. did it

17. I had to buy ______of these books because I didn’t know which one was the best.

　　　 A. both　　　　　　　　　　 B. none　　　　　　　　　　 C. neither　　　　　　　　　 D. whole

16. _______ you call me to say you are not coming, I’ll see you at the theatre.

　　　 A. If　　　　　　　　　　　　 B. Whether　　　　　　　 C. Until　　　　　　　　　　 D. Unless