题目内容
【题目】It is pretty well understood controls the flow of carbon dioxide in and out the atmosphere today.
that
when
what
how
【答案】C
【解析】分析句子结构可知,本句是一个含有主语从句的复合句。it为形式主语;“ controls the flow of.”为主语从句,而主语从句中缺少主语,引导词只能是what。
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