1.who指人，在從句中做主語
(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，在定語從句中充當賓語，常可省略。
(1) Mr. Liu is the person (whom) you talked about.
註意：關系代詞whom在口語和非正式語體中常用who代替，可省略。
(3) The man who/whom you met just now is my friend.
3. which指物，在定語從句中做主語或者賓語，做賓語時可省略
(1) Football is a game which is liked by most boys. ( which 在句子中做主語)
(2) This is the pen (which) he bought yesterday. ( which 在句子中做賓語)
4. that指人時，相當於who或者whom；指物時，相當於which。
在賓語從句中做主語或者賓語，做賓語時可省略。
(5) The people that/who come to visit the city are all here. (在句子中做主語)
(6) Where is the man that/whom I saw this morning? (在句子中做賓語)
5. whose通常指人，也可指物，在定語從句中做定語
(1) He has a friend whose father is a doctor.
(2) I lived in a house whose roof has fallen in.
whose指物時，常用以下結構來代替
(3)The classroom whose door is broken will soon be repaired.
=The classroom the door of which is broken will soon be repaired.
(5)Do you like the book whose color is yellow?
=Do you like the book the color of which is yellow?