名词性从句在句中充当名词的功能。

作主语： What he said was surprising.

作宾语： I don't know where she lives.

作表语： The problem is that we lack funding.

引导词： that, what, whether/if, who, where, when, how, why

注意： 宾语从句中的 that 可省略：I think (that) she is right.