定语从句中以who和whom引导的有什么区别?

定语从句中的who和whom叫做关系代词。其中who在定语从句中充当主语，whom充当宾语。但注意：who可以代替whom作宾语，但whom 不可代替who做主语。
The man who is standing there is my teacher.
The man who/whom you saw just now is my teacher.

WHO 代的是从句中的主语。
WHOM代从句中的并语。
比如：
She is the girl whom I am falling in love with.
Shi is Mary who is my mother.

简单地说就是他们所充当的句子成分是不一样的楼层:2
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