that(代词)作宾语时，有些情况下不能省略。
如，①直接跟在介词后作宾语时不能省略。介词+whom/which。
②在非限制性定语从句中不能省略。参看
例句（省略连词that）下列例句中的括号表示可以省略。
It is a pity (that) you don’t know Russian.（主语从句时省略that）
I hear (that) he has join the club.（宾语从句时省略that）
I’m afraid (that) I’ve made a mistake.（宾语从句时省略that）
The reason is (that) you don’t trust her.（表语从句时省略that）
例句（省略代词that）
The man (who(m)/that) we met yesterday used to be my schoolmaster.（作宾语时省略that）
The novel (which/that) he reads is borrowed from the library.（省略代词which/that）
He is no longer the lazy boy (that) he was.他不再是以前那个懒孩子了。（作表语时省略that）
