20. When ____ comes to repairing a machine, I have little knowledge of it.

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

19. Try to ____ at least half an hour each day for learning new vocabulary, and you’ll know more words.

　 A. set aside　　　　　　　 B. take up　　　　　　　 C. put away　　　　　 D. turn out

18. Creating world peace is a rather difficult goal, ____ calls for efforts of many generations.

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

17. Alone in a deserted house, he was so busy with his research work that he felt ____ but lonely.

　 A. nothing　　　　　　　 B. anything　　　　　　 C. all　　　　　　 D. everything

16. The troops ____ on for three days and nights. The soldiers are in great need of rest.

　 A. had marched　　　　　　　 B. have been marching　　　　　 C. marched　　　　　　 D. are marching