在复合句中充当主语的从句。

　　1.that引导主语从句

　　that引导主语从句时不同于其他的连词，既无词义也不作成分，只起单纯的连接作用，且通常不可以省。为了强调that引导的主语从句而置之于句首时，that不可省。

　　①That the driver could not control his car was obvious.

　　②That she was chosen made us very happy.

　　③That he will come is certain.

　　④That he would take the risk is true.

　　⑤That he should have married her isn't surprising.

　　★通常，that引导主语从句时用it做形式主语，把从句置于句尾，此时that有时可省。例如：

　　①It was obvious that the driver could not control his car.

　　②It made us very happy that she was chosen.

　　③It is certain that he will come.

　　④It is true that he would take the risk.

　　⑤It isn't surprising (that) he should have married