Cars play an important role in modern life but they also cause many problems like air po

问题补充：

Cars play an important role in modern life, but they also cause many problems like air pollution.

A. should

B. can

C. must

D. will

答案：

A. should

(答案→)B. can

C. must

D. will

解析：考查情态动词的用法。should应该，can有时候可能会，must必须，will将会，句意：汽车在相待生活中起着非常重要的作用，但是，他们有时候可能也会引起许多为题像空气污染。故选B。