主语从句
1、定义：先找到句子的谓语,主句的谓语前面的从句,叫做主语从句.
Why he left wasn't important.(wasn't是主句的谓语动词,why he left做主语从句)
That she became an artist may have been due to her father's influence.(may have been due是主句的谓语动词,that she became an artist做主语从句)
2、借助形式主语it,主语从句放在后面
①由that引导的主语从句可以放在主语的位置,这时that不可以省略.例如：That prices will go up is certain.
that主语从句放在句首的情况不是很常见,绝大部分主语从句都借助形式主语it,主语从句放在后面.
It is strange that he knows nothing about it.
It is a pity that he can't swim.
It happened that he wasn't in that day.
It is said that there has been an earthquake in India.
在口语中,用it做形式主语时,主语从句的that可以省略.
②wh-疑问词引导的主语从句,可以放在句首(第一组),也可以借助形式主语it(第二组).
第一组：When he'll be back depends much on the weather.
How it was done was a mystery.
Whether we'll succeed remains to be seen.
第二组：It is uncertain whether the game will be held.
It's a puzzle how life began.
It doesn't matter much where we live.
Is it known where he went?