什么是主语从句和同位语从句

主语从句是整个主句的主语。它的位置一个是在整个主句之前，一个是在后面用it 做形式主语。如：What he said is true.(what he said是主语从句)。

It is certain that he will come.(that he will come是主语从句)。

而同位语从句是对一名词或代词的解释说明。

它的位置在这一名词或代词之后，有的也被很短的谓语动词隔开。

如 The news that he will come is true.(that he will come是同位语从句）。

Word came that we will have an examination.(that we will have an examination是同位语从句)。