how和what在从句中的区别和用法

what = all that/ the thing that/ the person that.只引导主从,宾从,表从,不能引导定从和同位从,即what前面不能有名词。既起连接作用,又在从句中充当主、宾、表语的成分。即：what+不完整句子，做主从，宾从，表从。
How = in what way,如果宾语从句的谓语动词是不及物动词,并且是指方式和状态的,您就用how,因为how在宾语从句中作状语,常指方式和状态.
what连接代词,必须代替从句中的主/宾/表语,意为“什么”.例：I don’t know what to do.
how连接副词,必须代替从句中的方式状语,意为“如何,怎样”.例：I don’t know how to do it.

例如：
1. You can change anything to see () the car would look.
【How】，根据句义可知，是“看起来怎么样”，若look改为look like，则选what，作look like 宾语“看起来像什么”
2.Ask them what the boy had done worthy of () they were doing to him.
问问他们，这个男孩到底作了什么，值得他们这样对待他。
【What】，比较明显的是，of的从句是作worthy of的宾语，而引导词又是作宾语从句中谓语were doing的宾语，所以只能用what。