在以下情况中，that不能省略。
（1）and 连接两个或两个以上的
宾语从句时，第一个that可以省略也可以不省，但其它不能省略，以免产生误会
(2) that引导的宾语从句放在except ,but 等介词后面的时候,that不能省略.He is a good student except that he is a little careless.
(3) that 引导的宾语从句放在句首起强调作用的时候,that不能省略.That he ever said such a thing I simply don’t believe.
(4) 主句
谓语动词和that引导的宾语从句之间有插入的时候,that不能省略Everyone could see , I believe , that Tom was really afraid .
(5) it 作形式宾语时,that 引导的宾语从句中的that不能省略.We thought it strange that Xiao Wang did not come yesterday.
(6) 在对话中简短回答时,如果that引导的宾语从句独立出现,that不能省略.---What did he say ?
---That he won the first prize in the game .
(7) 在可接双宾语动词后that引导的宾语从句作直接宾语的时候,that不能省略.The foreign friend tells us that Chinese is one of the most difficult languages to learn .
(8) 在that引导的宾语从句之前或之后紧接着一个状语的时候,that不能省略.He suddenly caught sight of the boy and realized at once that he had seen him before.
(9) 在直接引语中,that引导的宾语从句与主句隔开的时候,that不能省略,.“I’m sorry to say,” he said ,“that you are not the suitable person”