that可以起连接词作用，有时有意义，有时没有意义。可以引导：1.名词性从句，即：宾语从句，主语从句，表语从句，同位语从句；2.定语从句，that作定语从句主语时不能省略，作宾语时可以省略；例如

1.The news that he had passed the exam made his parents very happy.(同位语从句,that不能省略)

2.The story book that/x you bought me is very interesting.(定语从句，that可以省略)

3.That he had been to Beijing is true.(主语从句，that不能省略)

4.The truth is that he has never been to Beijing.(表语从句，that不能省略)