what引导名词性从句，.表示……的东西或事情；
例如：
They’ve done what they can to help her.他们已经尽力帮助了她。
表示……的人或的样子：
He is no longer what he was.他已经不是以前的那个样子。
相关介绍
表示“……的数量或数目”：
Our income is now double what it was ten years ago.我们现在的收入是10年前的两倍。
The number of the students in our school is ten times what it was before liberation.现在我校学生的数量是解放前的10倍。
表示“……的时间”：
After what seemed like hours he came out with a bitter smile.似乎过了几个小时他才苦笑着出来。
The young girl was too frightened to speak, standing there for what seemed like hours.小女孩吓得不敢说话，在那儿站了几个小时。
表示“……的地方”：
This is what they call Salt Lake City.这就是他们称为盐湖城的地方。
In 1492, Columbus reached what is now called America.1492年哥伦布到达了现在所称的美洲大陆。
用法说明
(1) 这样用的what相当于“先行词+关系代词”，所以其前不能有先行词：
你喜欢什么就拿什么吧。
正：You can have what you like./ You can have everything (that) you like.
误：You can have everything what you like.
(2) 有时what 可用作限定词，其后修饰一个名词：
I gave him what books I had.我把我所有的书都给他了。
He gave me what money he had about him.他把身边带有的钱全给了我。
(3) What 后的名词可以是复数名词或不可数名词，但通常不能是单数可数名词：
误：I gave him what book I had.
(4) What后接不可数名词时，有时可有little修饰。注意区别：what+不可数名词=所有的都，what little+不可数名词=虽少但全部。如：
I spent what time I had with her.我所有的时间都是与她一起度过的。
I spent what little time I had with her.我仅有的一点时间都是与她一起度过的。
