The passage mainly discusses __

A． the economic impact on air pollution

B． what constitutes an air pollutant

C． how much damage air pollutants can cause

D． the quantity of compounds added to the atmosphere

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参考答案

答案解析

定位：根据题干信息The passage mainly discusses可知本题考查文章的主旨，需通观全文。
解析：四项分别为：空气污染的经济影响、空气污染物的构成、空气污染物会产生多大的危害、加入到大气中混合物的数量。比较可知B项较符合本文所介绍的主要内容，文章主要介绍了空气污染物，包括人类生产和大自然产生这两个来源。

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