3. 主语从句不可位于句首的五种情况：

(1)if 引导的主语从句不可居于复合句句首。

(2)It is said /reported…结构中的主语从句不可提前。例如：

正确表达：It is said that President Jiang will visit our school next week.

错误表达：That President Jiang will visit our school next week is said.

(3)It happens/occurs…结构中的主语从句不可提前。例如：

正确表达：It occurred to him that he failed in the examination.

错误表达：That he failed in the examination occurred to him.

(4)It doesn’t matter how/whether …结构中的主语从句不可提前。例如：

正确表达：It doesn’t matter whether he is wrong or not.

错误表达：Whether he is wrong or not doesn’t matter.

(5)含主语从句的复合句是疑问句时，主语从句不可提前。例如：

正确表达：Is it likely that it will rain in the evening?

错误表达：Is that will rain in the evening likely?

4. what 与that 在引导主语从句时的区别

what 引导主语从句时在句时在从句中充当句子成分，如主语.宾语.表语，而that 则不然。例如：

a) What you said yesterday is right.

b) That she is still alive is a consolation

二.宾语从句

宾语从句就是在复合句中作宾语的名词性从句，通常放在主句谓语动词 (及物动词) 或介词之后。

1. 作动词的宾语

(1) 由that引导的宾语从句(that 通常可以省略), 例如：

I heard that be joined the army. 我听说他参军了。

(2) 由what, whether (if) 引导的宾语从句，例如：

a) She did not know what had happened.　她不知道发生了什么。

b) I wonder whether you can change this note for me.　我想知道你是否能帮我改一下笔记。

(3) 动词+间接宾语+宾语从句。例如：

She told me that she would accept my invitation.　她对我说她会接受我的邀请。

2. 作介词的宾语，例如：

Our success depends upon how well we can cooperate with one another.　我们的成功取决于我们之间的合作。

3. 作形容词的宾语，例如：

I am afraid (that) I’ve made a mistake.　我恐怕我已经犯了一个错误。

注意：that 引导的从句常跟在下列形容词后作宾语：anxious, aware, certain, confident, convinced, determined, glad, proud, surprised, worried, sorry, thankful, ashamed, disappointed, annoyed, pleased, hurt, satisfied, content 等。也可以将此类词后的that从句的看作原因状语从句。