Air, which (it is) a mixture of elements oxygen and nitrogen (and compounds) water and carbon dioxide, also (contains) small qua

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问题 Air, which (it is) a mixture of elements oxygen and nitrogen (and compounds) water and carbon dioxide, also (contains) small quantities of (many other) substances.

选项 A、it is
B、and compounds
C、contains
D、many other

答案A

解析
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