定语从句。
定义。
an exciting match:形容词可以放在名词之前作定语，来修饰名词the book in my hand:介词短语可以放在名词之后作定语，来修饰名词。
但如果修饰名词的定语不是某一个词或短语，而是一个句子时，我们就要使用定语从句。
定语从句通常跟在所要修饰的中心名词（先行词）之后，由关系代词或关系副词引导。
定语从句相当于形容词或者介词短语的作用。
注意。
1.从句相当于整个句子的一个成分，因此，从句不能单独使用。
She saw that he was sleeping.(宾语从句)I am reading the article which is about your experience in the UK.(定语从句)2.先行词定语从句所修饰的词叫“先行词”，因为它总是处在定语从句的前头，比定语从句先行一步。
先行词通常为人、物或者是事情。
e.g. I am reading the article that is about your experience in the UK.3.关系词从意义上说：先行词定语从句的组成部分从结构上说：先行词不在从句中出现引导定语从句，并取代先行词在从句中的成分e.g. I am reading the article that is about your experience in the UK.关系词的功能：1.关系词作主语（动作发出者）The trees are on the school campus. They have lost their leaves.The trees which are on the school campus have lost their leaves.2. 关系词作宾语（动作接受者）We saw the student just now. He is the best runner in our school.The student whom we saw just now is the best runner in our school.3. 关系词作表语Jack used to be a lazy boy. He is no longer a lazy boyJack is no longer the lazy boy that he used to be.4. 关系词作定语（通常为所有格）She has a brother. I can’t remember his name.She has a brother whose name I can’t remember.5. 关系词作状语（时间状语、地点状语、原因状语）The school is in Shenzhen. He studies in the schoolThe school where he studies is in Shenzhen.4.定语从句分为限制性定语从句和非限制性定语从句。
关系词。
关系代词(relative pronouns)who, whom, which, that, as, whose等跟在先行词的后面，指代先行词，引出定语从句。
在从句中充当主语、宾语、表语、定语的作用。
who的用法先行词必须是人，作主语和宾语e.g. The man who spoke at the meeting this morning is a famous lawyer. The girl who you saw just now is Jane.作宾语时，可用whom, that替换, 可以省略。
whom的用法先行词必须是人，作宾语。
通常可以省略e.g. The girl whom / who / that you saw just now is Jane.which的用法先行词必须是事物，作主语和宾语e.g. This is the book which / that was written in easy English by our English teacher.作主语时，关系词不可省略。
The pictures (which / that) he drew in the 1980s are on show.作宾语时，关系词可以省略。
注意(whom & which)：whom & which做介词宾语时，介词常可提前，即介词+whom/which+从句，此时whom & which不能由who或that代替，不能省略。
e.g. This is the man from whom your son always begs money.The chair on which she is sitting is made of wood.但当介词置于从句末尾时，whom可以由who或that代替，which可由that代替，都能省略。
e.g. This is the man (whom / that / who) your son always begs money from. 有一些动词短语中的介词是固定搭配，不可拆开，一般还是放在动词之后，不提前。
He is the student who the teachers are looking for.The number of the children who she takes care of is 30.动词短语是否可以拆分，关键看拆分后与拆分前的意思是否相同。
如果意思不变，可以拆分，否则不行。
that的用法1)that可作定语从句中的主语（取代who或which），宾语（取代who或whom或which）2)关系代词作表语，必须使用that，指代人或物，可以省略。
e.g. My father is no longer the man (that) he was.My hometown is not the small town that it used to be twenty years ago.3)that的特殊用法必须使用that的情况。
①当先行词是人+事物时。
e.g.They talked about the teachers and schools that they had visited.The police had great trouble in diverting the men and the cars that had blocked the way.②当先行词跟在系动词be后作表语，或关系词本身作定语从句的表语时，关系代词必须用that，但也可以省略e.g.My father is no longer the man (that) he was.He thought his daughter would be the dancer (that) she always wanted to be. It’s a book (that) will help you a great deal.③当先行词被形容词最高级、序数词如the first, the last 等词修饰时。
e.g. This is the best film that I have ever seen.This is the first choice that I have made.She is the most careful girl that I have ever known.This is the last letter that I received from him.④当先行词前面有the only, the very, one of, any, no, every, few, little等词修饰时。
e.g. The only person that seems to know the truth is Doctor Brown.Any person that wants to succeed must work hard.There is no difficulty that we can not overcome.I have read all the books that can be borrowed here.⑤当先行词本身为不定代词如anything, something, nothing, everything, all, much, few, little, none, the one时。
e.g.All that I want is peace and stability.There is little that I can do.There is nothing that I can tell you.I have tried everything that I can think of.I do not mean this one. I mean the one that was bought yesterday.注意：anybody, nobody, everybody等不在此列。
不能使用that的情况。
①当定语从句前有介词时，关系代词不能用that。
②that不能用于非限制性定于从句。
③当先行词为one, ones, anyone, those, 指人时，用who。
e.g.Those who learn not only from books but also through practice will succeed.④当先行词是he时，用who。
(多谚语)e.g.He who plays with fire gets burnt.He who laughs at last laughs best.⑤当先行词本身是that时，用which或who避免重复不能用于非限制性定于从句。
e.g.What’s that which flashed in the sky just now?whose的用法whose作定语从句中的定语，表示所修饰的“某（些）人的”或“某物的”。
e.g.The boy whose name is Tom is the top student in my class.Look at the house whose roof is red.注意：当whose指代物时，whose+从句结构=…of which+从句=of which the…+从句e.g. Look at the house whose roof is red.Look at the house, the roof of which is red.Look at the house, of which the roof is red.as的用法1)as用于限制性定语从句so …as；such…as；the same…as；2)as用于非限制性定语从句。
