定语从句
一、语法解释
定语从句：修饰名词或代词的从句。换句话说，名词、代词后的从句叫定语从句。 先行词：被定语从句修饰的名词、代词、甚至词组或句子叫先行词。 关系词：引导定语从句的词叫关系词。
关系词分两种： 一是关系代词that, which, who, whom, whose, as等(在定语从句中担任主、宾、表、定语成分)； 二是关系副词where, when, why等(在定语从句中担任状语成分)。
关系词的三个功能：1. 连接功能（连接先行词与定语从句）；
2. 担任功能（在定语从句中担任主、宾、表、定、状语）； 3. 替代功能（在定语从句中代替先行词）
e.g. A plane is a machine. The machine can fly.↓
A plane is a machine, and the machine can fly.↓ A plane is a machine that can fly.
二、关系代词引导的定语从句
1.who指人，在从句中做主语，也可作宾语。
e.g. The boys who are playing football are from Class One. e.g. 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。
e.g. Mr. Liu is the person (whom) you talked about on the bus. e.g. 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。 e.g. The man who/whom you met just now is my friend.
3. which指物，在定语从句中做主语或者宾语，做宾语时可省略。
e.g. Football is a game which is liked by most boys. e.g. 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。在宾语从句中做主语或者宾语，做宾语时可省略。
e.g.The number of the people that/who come to visit the city each year rises one million. e.g. 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。
e.g. He has a friend whose father is a doctor. e.g. I once lived in a house whose roof has fallen in.
引导定语从句的“whose＋名词”，有时可与of which或of whom互换：
e.g. The classroom whose door(= the door of which) is broken will soon be repaired. e.g. Do you like the book whose cover(= the color of which) is yellow?
三、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。 e.g. The school (that/which) he once studied in is very famous.↓ The school in which he once studied is very famous.
e.g. Tomorrow I will bring here a magazine (that/which) you asked for.↓ Tomorrow I will bring here a magazine for which you asked.
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 e.g. This is the watch which/that I am looking for. (T) e.g. This is the watch for which I am looking. (F)
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
e.g. The man with whom you talked is my friend. (T) e.g. The man who/that you talked with is my friend. (F)
e.g. The plane in which we flew to Canada is very comfortable. (T) e.g. 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
e.g. He loved his parents deeply, both of whom are very kind to him. e.g. In the basket there are quite many apples, some of which have gone bad.
四、关系副词引导的定语从句
1. when指时间，在定语从句中做时间状语 。
e.g. I still remember the day when I first came to the school. e.g. The time when we got together finally came. 2. where指地点，在定语从句中做地点状语。
e.g. Shanghai is the city where I was born.
e.g. The house where I lived ten years ago has been pulled down. 3. why指原因，在定语从句中做原因状语。
e.g. Please tell me the reason why you missed the plane. e.g. I don't know the reason why he looks unhappy today.
注意：关系副词引导的从句可以由“介词+关系代词”引导的从句替换。 e.g. The reason why(for which) he refused the invitation is not clear.
e.g. From the year when(in which) he was going to school he began to know what he wanted when he grew up.
五、限制性定语从句和非限制性定语从句 1. 限制性定语从句举例：
e.g. The teacher told me that Tom was the only person that I could depend on. e.g. China is a country which has a long history. 2. 非限制性定语从句举例：
e.g. His mother, who loves him very much, is strict with him.
e.g. China, which was founded in 1949, is becoming more and more powerful. 要注意区分以下几个句子的不同：
e.g. His brother who is now a doctor always encourages him to go to college. 他那当医生的哥哥常鼓励他要考上大学。（他还有其他的哥哥）
e.g.His brother, who is now a doctor, always encourages him to go to college. 他的哥哥是当医生的，常鼓励他要考上大学。（他只有一个哥哥）
六、难点分析
（一）限制性定语从句只能用that 的几种情况
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。
e.g. Have you taken down everything that Mr. Li has said? e.g. There is little that I can do for you.
注意：这种情况下，当先行词指人时，偶尔也可以用who e.g. Any man that/who has a sense of duty won't do such a thing. 2. 当先行词被序数词修饰 。
e.g. The first place that they visited in London was the Big Ben.
