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。