1.that引导宾语从句无意义，不充当句子成分常省略。但下列情况除外：

(1)介词宾语从句的that不省略

(2) and连接的几个从句，第二个从句以后的从句的that不省略。

He told me that he had two sons and that they both had gone to college.

(3)在动词+it+宾语补足语+宾语从句结构中，that不省略。

I heard it said that he had gone abroad

We found it impossible that he could finish it in such a short time

2.Whether ,if 引导宾语从句：两词可互换，但是下列情形除外：

(1)whether从句中有or not

(2)whether从句做介词宾语

Everything depends on whether you agree with us

3.许多带复合宾语的句子，宾语从句经常移到句子后部，而用it做形式宾语。结构常是：