一、 概念：
he is the boy who often goes to school late.
先行词关系词定语从句。
二、原则：
a.定语从句必须紧紧地跟在先行词后面，限制修饰先行词。
b.定语从句必须用关系词来引导。
c.关系词在定语从句中作一个句子成分。
三、下列定语从句只能用that来引导：
1.先行词为形容词最高级所修饰。
this is the longest bridge that i h**e ever seen.
2.先行词为序数词所修饰。
i happened to be the thousandth guest that visited the great hotel.
this is the first composition that he has ever written in english.
3.先行词既包括人又包括物。
they talked of things and persons that happened in the school.
he talked about the teachers and schools that he had visited.
4.主句是who或which开头的特殊疑问句中的定语从句。
who is the man that came this morning?
which is the bag that you lost?
5.先行词为the only, the very, the last, the same所修饰的定语从句。
he is the very person that the police are looking for.
this is the only thing that i can remember.
6.先行词是everything, nothing, something, all, little, much,everybody等不定代词。
tell us everything that you know, please.
is there anything that you don’t understand?
7.先行词被all, every, no, some, any, little, much修饰时。
all that glitters is not gold.
i’ve read all the books that you g**e me.
四、“介词+ 关系词” 及关系副词when, where, why
1). the box is full of bottles. he is standing on the box.
---the box on which he is standing is full of bottles.
the box where he is standing is full of bottles.
2). this is the train. we work on the train.
---this is the train on which we work.
this is the train where we work.
3). i know the reason. she did it for the reason.
---i know the reason for which she did it.
i know the reason why she did it.
4). the man is our school master. you shook hands with the man just
now.---the man with whom you shook hands is our schoolmaster.
5). the pen is made in shanghai. she is writing with the pen.
---the pen with which she is writing is made in shanghai.
不能拆开的词组： look for / look after / catch hold of /take care of / put on / take off…….
五、非限制性定语从句只对先行词起补充，说明的作用，常用逗号分开。关系代词用who(m), which，关系副词用where ,when. 非限制性定语从句不能用that来引导。
this was the american civil war, which lasted 4 years before the north won in the end.
he was taken to another room, where he found a wounded boy, who was dying.
六、as 作为关系代词， 习惯上用于下列词组：
the same...as such ..as as ..as， so…as
1. take as many books as you want.
2. here is so big a stone as no man can lift.
3. he read such books as will make him wiser.
4. the town is about the same distance from nanjing as yangzhou is.
as 用于非限制性定语从句，常见以下句型：
as you know, as we h**e seen, as is known to all, as anybody can see, as was expected, as we can imagine, as has been pointed out
as与which的用法区别：as与 which在非限制性定语从句中，都可指代整个主句，但as引导的从句可放在主句的句首， 句中或句尾， 而 which引导的从句只可放在主句的句尾。
as we h**e seen, oceans cover more than 70 percent of the earth.
oceans cover more than 70 percent of the earth, as we h**e seen.
she was awarded a gold medal, which the whole family considered a great honour.
七、the same…as, the same …that 的区别。
this is the same bag as i lost yesterday. （相似的事物）
i am wearing the same coat that i wore yesterday. （同一事物）
八、定语从句和同位语从句的区别：
定语从句相当于形容词作定语， 对先行词加以限制或修饰，同位语从句相当于名词，对先行词加以补充或说明，连接词that在定语从句中充当某个成分，而that在同位语从句不充当句子成分。
the promise that my uncle g**e me made us happy. （定语从句）
the promise that my uncle would give me a new bike made us happy. (同位语从句)
the news that they had won came.
九、 关系代词what和that, which的区别：
先比较下列句子中的what和that:
he told us the things that he had seen.
-> he told us what he had seen.
this is the words which i said.
-> this is what i said.
可以看出what 实际上等于是 “the thing that(which)”,即 “先行词+关系词”. 因此在句中如果已有先行词，则不能用what，而只能用that(which)，如没有先行词，则用what。what是一个没有先行词的关系词。
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