2. which作宾语时，根据先行词与定语从句之间的语义关系，先行词与which之间的介词不能丢。
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，这些词包括当先行词是anything, everything, nothing , none等不定代词时，或者是由every, any, all, some, no, little, few, much等修饰时等，这时的that常被省略还有先行词前有序数词或形容词最高级修饰时，或先行词就是序数词或最高级时。以及先行词中既有人又有物时。
还有句中前面有which时，都只能用that
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. whose是关系代词，修饰名词作定语，相当于所修饰成分的前置所有格。它引导的从句可以修饰人和物， 当它引导的从句修饰物体时， 可以与 of which 调换，表达的意思一样。
二、关系副词（在句中作状语）
关系副词=介词+关系代词。
why=for which
where=in/ at/ on/ .which (介词同先行词搭配)
when=during/ on/ in/ .which (介词同先行词搭配)
1. where是关系副词，用来表示地点的定语从句。
2. 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 h**e 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 towels, soap, toothbrush etc。
3. 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。
there is somebody here who wants to speak to you. 这里有人要和你说话。
二）非限定性定语从句。
非限定性定语从句的作用是对所修饰的成分作进一步说明，通常是引导词和先行词之间用逗号隔开，将从句拿掉后其他部分仍可成立。
1. which引导的非限定性定语从句来说明前面整个句子的情况或主句的某一部分。
2.当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的，例如：
charles smith, who was my former teacher, retired last year. 查理·史密斯去年退休了，他曾经是我的老师。
my house, which i bought last year, has got a lovely garden. 我去年买的的那幢房子带着个漂亮的花园。
this novel, which i h**e read three times, is very touching. 这本**很动人，我已经读了三遍。
3.非限制性定语从句还能将整个主句作为先行词， 对其进行修饰， 这时从句谓语动词要用第三人称单数，例如：
he seems not to h**e grasped what i meant, which greatly upsets me. 他似乎没抓住我的意思，这使我心烦。
liquid water changes to vapor, which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。
4. 有时as也可用作关系代词。
5. 在非限定性定语从句中，不能用关系副词why和关系代词that，而用who, whom代表人，用which,whose代表事物。；
三）关系代词引导的定语从句。
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。（注：who和whom已无太大区别，可以通用。）
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.
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.
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.
指物，在定语从句中做主语或者宾语，做宾语时可省略。
1) football is a game which is liked by most boys.
2) this is the pen (which) he bought yesterday.
4. 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.
6) where is the man that/whom i saw this morning?
5. whose通常指人，也可指物，在定语从句中做定语。
1) he has a friend whose father is a doctor.
2) i once lived in a house whose roof has fallen 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 color is yellow?
6) do you like the book the color of which is yellow?
四）注意。介词+关系代词引导的定语从句关系代词在定语从句中做介词宾语时。
从句常由介词+关系代词引导。
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 h**e often talked about.
6) we’ll go to hear the famous singer about whom we h**e 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＝正确)
2) this is the watch for which i am looking. (f＝错误)
2. 若介词放在关系代词前，关系代词指人时用whom，不可用who或者that；指物时用which，不能用that；关系代词是所有格时用whose
1) the man with whom you talked is my friend. (t)
2) the man with that you talked 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 h**e gone bad.
3) there are forty students in our class in all, most of whom are from big cities.
关系代词。关系代词（一般情况下）that 可用who ,whom 和which在从句做主语，谓动词的宾语，但是不能做介词的宾语。
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