that引導的從句有如下：
1、從句的主語是that時，that不能省。
We know that that is an important meeting．
2、動詞後接多於兩個由that引導的賓語從句時，第壹個that可省，但後面的that不可省。
He said (that) you were too young to understand the matter and that he was asked not to tell you.
3、that引導的賓語從句中緊跟復合句從句時，that不能省。
I think that if you have lost the library book, you must pay for it．
4、當主句的謂語與賓語從句之間有插入語時，that不能省。
He says, in the newspaper, that English is getting more and more important．
5、當that從句是雙賓語中的直接賓語時，that不可省。
I can’t tell him that his mother died.