The problem of air pollution is being more serious the increasing number of cars.
A. as for
B. because
C. as a result
D. as a result of
网友回答
A. as for
B. because
C. as a result
(答案→)D. as a result of
解析：本题的含义为由于车子数量急剧增加的结果，空气污染的问题变得更加严重，as a result of 表示由于……的结果的含义，故本题选D。