1. that即可代表事物也可代表人，which代表事物;它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从句中作宾语则不能省略。而且，如果which在从句中作“不及物动词+介词”的介词的宾语，注意介词不要丢掉，而且介词总是放在关系代词which的前边，但有的则放在它原来的位置 。
3. 代表物时多用which，但在带有下列词的句子中用that而不用which，这些词包括all, anything, much等，这时的that常被省略 。
4. who和whom引导的从句用来修饰人，分别作从句中的主语和宾语，whom作宾语时，要注意它可以作动词的宾语也可以作介词的宾语 。
5. where是关系副词，用来表示地点的定语从句 。
6. when引导定语从句表示时间[注]值得一提的是，表示时间“time"一词的定语从句只用when引导，有时不用任何关系代词，当然也不用that引导 。
By the time you arrive in London, we will have stayed there for two weeks. I still remember the first time I met her. Each time he goes to business trip, he brings a lot of living necessities, such as towers, soap, toothbrush etc.
8. 当从句的逻辑主语是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing时，常用there is来引导。
1.定语从句：修饰一个名词或代词的从句称为定语从句，一般紧跟在它所修饰的先行词后面。2.关系词：引导定语从句的关联词成为关系词关系词有关系代词和关系副词。关系代词有that, which, who, whom, whose, as等;关系副词有where, when, why等。关系词常有3个作用：1，引导定语从句。2，代替先行词。3，在定语从句中担当一个成分。
(1) The boys who are playing football are from Class One.
(2) Yesterday I helped an old man who lost his way.
(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.
(3) The man who/whom you met just now is my friend.
(1) Football is a game which is liked by most boys.
(2) This is the pen (which) he bought yesterday.
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.
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.
(5) The number of the people that/who come to visit the city each year rises one million.
(6) Where is the man that/whom I saw this morning?
(1) He has a friend whose father is a doctor.
(2) I once lived in a house whose roof has fallen in.whose指物时，常用以下结构来代替。
(3) The classroom whose door is broken will soon be repaired.
(4) The classroom the door of which is broken will soon be repaired.
(5) Do you like the book whose cover is yellow?
(6) Do you like the book the color of which is yellow?
(1) The school (that/which) he once studied in is very famous.
(2) The school in which he once studied is very famous.
(3) Tomorrow I will bring here a magazine (that/which) you asked for.
(4) Tomorrow I will bring here a magazine for which you asked.
(5) We’ll go to hear the famous singer (whom/that/who) we have often talked about.
(6) We’ll go to hear the famous singer about whom we have often talked.
注意：1. 含有介词的动词短语一般不拆开使用，如：look for, look after, take care of等。
(1) This is the watch which/that I am looking for. (T)
(2) This is the watch for which I am looking. (F)
(1) The man with whom you talked is my friend. (T)
(2) The man who/that you talked with is my friend. (F)
(3) The plane in which we flew to Canada is very comfortable. (T)
(4) The plane in that we flew in to Canada is very comfortable. (F)
3. “介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词或者数词。
(1) He loved his parents deeply, both of whom are very kind to him.
(2) In the basket there are quite many apples, some of which have gone bad.
(3) There are forty students in our class in all, most of whom are from big cities.
(1) I still remember the day when I first came to the school.
(2) The time when we got together finally came.2. where指地点，在定语从句中做地点状语。
(1) Shanghai is the city where I was born.
(2) The house where I lived ten years ago has been pulled down.
(1) Please tell me the reason why you missed the plane.
(2) I don’t know the reason why he looks unhappy today.
(1) The reason why/ for which he refused the invitation is not clear,
(2) From the year when/in which he was going to school he began to know what he wanted when he grew up.
(3) Great changes have taken place in the city in which./where I was born.
(错)The tree, that is four hundred years old, Is very famous here.
We depend on the land from which we get our food.
We depend on the land that/which we get our food from.
(2) 只能用that作为定语从句的关系代词的情况 。
(a) 在there be 句型中，只用that，不用which。
(b) 在不定代词，如：anything, nothing, the one, all, much, few, any, little等作先行词时，只用that，不用which。
(c) 先行词有the only, the very,the same,the last,just修饰时，只用that。
Is this the book that you borrowed in the library?
Who that break the window should be punished.
All that is needed is a supply of oil.
Finally, the thief handed everything that he had stolen to the police.
1.当先行词是anything, everything, nothing (something 除外), few, all, none, little, some等代词时，或者是由every, any, all, some, no, little, few, much等修饰时。
(1) Have you taken down everything that Mr. Li has said?
(2) There seems to be nothing that seems impossible for him in the world.
(3) All that can be done has been done.
(4) There is little that I can do for you.
(4) Any man that/.who has a sense of duty won’t do such a thing.
(1) The first place that they visited in London was the Big Ben.
(1) This is the best film that I have seen.
4. 当形容词被the very, the only 修饰时。
(1) This is the very good dictionary that I want to buy,
(2) After the fire in his house, the old car is the only thing that he owned.
(3) Wang Hua is the only person in our school who will attend the meeting?
5. 当先行词前面有who, which等疑问代词时。
(1) Who is the man that is standing there?
(2) Which is the T-shirt that fits me most?
(1) Can you remember the scientist and his theory that we have learned?