21. In ancient China, people used to send smoke _____ to warn that the enemy were coming.
A. signs B. signals C. symbols D. marks
解析: 这个题考四个名词的比较, 其中: signs 迹象; signals 信号; symbols 象征; marks 分数.
22. The icy conditions made our travel dangerous. So _____ going by car we took the underground.
A. instead of B. in addition to
C. as well as D. at the cost of
解析: instead of 代替,而不是; in addition to 除了…之外(还有); as well as 也(除…之外), 既…又…; at the cost of 以…为代价. 这道题横线后面是动名词形式,所以选项C和D首先排除.
23. Sometimes my job is boring, but _____ I enjoy it.
A. by contrast B. by nature
C. on the whole D. on the average
解析: by contrast 与…相比,后面要跟with, by contrast with与…相比较; by nature 本性,生性; on the whole 总的来说; on the average 平均.
24. I’ll buy the clock _____ it costs.
A. what B. whatever C. where D. however
25. _____ Mr.Wilson is well again, he can travel.
A. Now that B. So far C. Though D. Even if
解析: Now that 既然; So far和现在完成时态连用.