以下情況不可省略：

　　1.that引導主語(yǔ)從句、表語(yǔ)從句、同位語(yǔ)從句時(shí)不能省略。

　　2.賓語(yǔ)從句不止一個(gè)時(shí),不能省略 如；they complain（that）they have to do homework from morning till night,that it is hard to study good,that they are very tired.是連續的賓語(yǔ)從句時(shí),第一個(gè)可省,后面都不行。

　　3.賓語(yǔ)從句與主語(yǔ)之間有插入語(yǔ)時(shí),不可省。如：the teacher said,happy and firmly(插入語(yǔ)),that we must do homework.

　　4.引導賓語(yǔ)從句是一個(gè)主從復合句。如：i belive that if i work harder,i will pass the exam.