If there aretrees the air in our city will becleaner.A. less; more B. more; moreC. more;

问题补充：

If there aretrees, the air in our city will becleaner.

A. less; more

B. more; more

C. more; much

D. much; more

答案：

A. less; more

B. more; more

(答案→)C. more; much

D. much; more

解析：less是little的比较级，表示更少的；more是much和many的比较级，表示更多的；much是许多，大量意思，修饰不可数名词。句意：如果有更多的树木，我们城市中的空气就会清新的多。结合语境可知前文表示对比，下文much用作副词修饰比较级，故选C。