Many cities issued a warning of air pollution for PM-2.5 readings, which becameConcern of

发布时间：2020-08-17 03:35:40

Many cities issued a warning of      air pollution for PM-2.5 readings, which became
     Concern of all the people
A. the; the
B. the;/
C. /;a
D. an;a

网友回答

A. the; the
B. the;/
(答案→)C. /;a
D. an;a
解析：第一个空，空气污染应是一个抽象的概念, 抽象名词前不用冠词；第二个空，表示泛指“关心的一件事”，故用不定冠词a。
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