Nowadays certain limit should be set on use of cars to reduce air pollution.A. /; theB. a;

问题补充：

Nowadays certain limit should be set on use of cars to reduce air pollution.

A. /; the

B. a; the

C. the; /

D. the; the

答案：

A. /; the

(答案→)B. a; the

C. the; /

D. the; the

解析：第一空填a，set a certain limit设定一定的限制，第二空填the，特指“汽车的使用”，句意：现在为了减少对空气污染，就有必要对汽车的使用设定一定的限制。选B项。