who是人。which是物，what=the thing that
名词性从句中 what which 怎么翻译
简单地说就是他们所充当的句子成分是不一样的
who 可以做主语，又可以做宾语
whom只能做宾语
who和whom在定语从句中作关系代词时：
1、who指人，在从句中做主语
(1) The boys who are playing football are from Class One.
(2) Yesterday I helped an old man who lost his way.
2、whom指人，在定语从句中充当宾语，常可省略
(1) Mr.Liu is the person (whom) you talked about on the bus.
(2) Mr.Ling is just the boy whom I want to see.
注意：关系代词whom在口语和非正式语体中常用who代替，可省略
当先行词前没有最高级，everything，anything，something，nothing时可用which或that，且从句后有介词时只能用which
例1：The girl which is eating ice cream is my sister.
例2：The chair which my father sits on is bought by me.
which也可作疑问词
例：Which is the shirt you bought yesterday?
