it is pretty well understood what controls the flow of carbo

学习时间:2026-08-14 05:37:23 阅读：5151

it is pretty well understood what controls the flow of carbon dioxide in and out today.what 引导什么从句，it是不是形式主语，如果是形式主语可以用what吗，可不可以用that what？

灵巧的奇迹

2026-08-14 05:37:23

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it是形式主语,what引导的是主语从句,是真正的主语。这里不能用that,两者的不同是what在从句中担当成分（这里做从句主语）,而that不担当任何成分,只起连接作用。例：It is true that the sun rises in the east。