形式主语，可以用whether来引导，有时也可以用if来引导。

Whether she will go there is not known

Whether I will accept the job is not decided.

It is not decided whether / if I will accept the job.

四．wh-疑问词引导的主语从句

　　用what；whatever；whoever；whichever引导主语从句时，不能用it做形式主语。但用when；where；why；wherever；whenever引导主语从句时，可以用it做形式主语。

What we need is your help.

What she said is not true.

Whatever I have is yours.

Whoever comes will be welcome.

Wherever she wants to go is not allowed.

Why he did this is not known.

It is not known why he did this.

It is still unknown when she will come.

表语从句

一．概述：

　　在复合句中充当表语成份的句子叫做表语从句。引导表语从句的连接词有连词that；whether；as if。疑问代词who；what；which。疑问副词when；where；why；how等。 e.g.

The trouble is that she has lost his telephone number.

The question is whether it is worth doing.

It looks as if it was going to snow.

That is where she was born.

That is how she did it.

That's why she was late.

二．that引导的表语从句

　　that引导表语从句时，在表语从句中没有任何意义，也不充当任何成分，只是单纯的连词，而且不能省略。

The fact is that the child is lying.

The trouble is that we are short of money.

The reason he did not come is that he was ill.

My opinion is that you should finish your homework first.

三．whether引导的表语从句

　　当表语从句为不确定语气时，用whether来引导。此时不能用if来代替。

The first question is whether it is true or not.

The question is whether people will buy it.

What I want to know is whether I should go there.

The question remains whether we can win the majority of the people.

四．wh-疑问词引导的表语从句

　　当表语从句为带有特定的疑问意义时，用wh-疑问词来引导。

The problem is how we could make him understand it.