who指人在从句中做主语
(1) The boys who are playing football are from Class One. 在踢足球的男孩们是一班的.
(2) Yesterday I helped an old man who lost his way. 昨天，我帮助了一个迷路的老人.
whom指人
在定语从句中充当宾语，常省略。（注：who和whom已无太大区别，基本可以通用。区别是who可以做主语而whom不可以，whom前可以加介词如to whom，但是who不可以）
(1) Mr. Liu is the person (whom) you talked with on the bus. 刘先生就是在公交车上和你聊天的那个人.
(2) Mr. Ling is just the boy(whom)I want to see. 凌先生恰巧就是我想见的那个男孩.
(3) The man who/whom you met just now is my friend. 你刚刚见到的那个人就是我的朋友.
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。
如果在从句中做宾语,就用whom或who.比如: He is the man whom/who I talk to. 他就是那个和我聊天的男人.
如果是在从句中作主语就只能用who.比如: He is the man who has an English book. 他就是那个有英语书的男人.
whose通常指人也可指物
在定语从句中做定语，表所有。
(1) He has a friend whose father is a doctor. 他有一个朋友的父亲是医生.
(2) I once lived in a house whose roof has fallen in.我曾经住在一座现在已经倒塌的房子中.
whose指物时通常以以下结构来代替
(3) The classroom whose door is broken will soon be repaired.那个门被打破的教室不久会被修复。
(4) The classroom the door of which is broken will soon be repaired.课堂门，被打破会不久被修复。
(5) Do you like the book whose color is yellow?你喜欢颜色是黄色的书吗?
(6) Do you like the book the color of which is yellow?你喜欢的书的颜色是什么？是黄色吗?
which指物
在定语从句中做主语，表语，定语或者宾语，做宾语时可省略。在非限制性定语从句中有“，”即可用which
(1) Football is a game which is liked by most boys. 足球是大多数男孩都喜欢的游戏.
(2) This is the pen (which) he bought yesterday. 这是他昨天刚买的钢笔.
that指人时
相当于who或者whom；指物时，相当于which。
在定语从句中做主语,表语或者宾语，做宾语时可省略。
(5) The number of the people that/who come to visit the city each year rises one million.数目的人民那个/谁来城市观光每年上升之一个百万
(6) Where is the man that/whom I saw this morning?那个男人在哪里/我看见谁了今天早上?