◎ 题干
As a recent survey states, people can hardly enjoy a clear blue sky        because of the high level of PM 2.5.
A.in troubleB.on purposeC.as usualD.in ruins
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“As a recent survey states, people can hardly enjoy a clear blue sky because of the high level of PM 2.5. A.in troubleB.on purposeC.as usualD.in ruins…”主要考查了你对  【介词和介词短语】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。