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