1．that
that在定语从句中可以指人也可以指物，
在从句中作主语或宾语，但不能放在介词后作介词宾语。如：
The eggs that I bought yesterday were not fresh.我昨天买的鸡蛋不新鲜。
I prefer dumplings that have just been cooked.
我更喜欢吃刚煮出来的饺子。
指物时that和which可以互换，但下面几种情况通常用that引导定语从句，不能用which。
（l）当先行词有最高级修饰或本身就是最高级时。如：
This book is the most difficult one that I have ever read. 这本书是我所读过的最难的一本书。
The best that I could do was to apologize
我能做的最好的事情就是道歉。
（2）当先行词有序数词修饰或本身就是序数词时。如：
Here are two students，the third that you want is to come in a minute.这儿有两个学生，你要的第三个学生一会儿就来。
The second school that I visited here was Yucai Middle School.我在这儿所参观的第二所学校是育才中学。
（3）当先行词是all，something，anything,little,much，none等不定代词时。如：
There is little that I can do to make up for the lost time.我没有办法弥补所丢失的时间。
All that is worth doing is worth doing well.
值得做的就值得做好。
（4）当先行词前有only，all，any，no等词修饰时。如：
There are no people that things must not happen to.没有人一生不出事。
The only thing that they could do was to sleep.
他们所能做的事就是睡觉。
（5）当先行词为表语时。如：
This is the school that I once studied at.
这就是我曾经上学的学校。
My father is no longer the man that he was.
我爸爸已经不是过去的样子了。
（6）当先行词既含有人又含有物时。如：
They talked about the persons and things that they remembered in the school.
他们谈论还能记起的在学校里的人和事。
The man and manners that he describes in his book are familiar.
他书中所描述的人以及所用的手法都很熟悉。
（7）句中有两个定语从句，其中第一个从句的关系代词已用了who或which时，第二个定语从句的关系代词用that。如：
Our English teacher is the man who is talking with the girl that is in red.我们的英语老师就是那位男子，他在和穿红衣服的女孩谈话。
We built a factory which produces fertilizer that is badly needed.
我们修建了一个工厂，生产急需的化肥。
（8）在以who开头的疑问句中。如：
Who is the boy that is standing at the gate？
门口站的那个男孩是谁？
Who was she that he danced with?
和他跳舞的那个女士是谁？
2.which
which在定语从句中指物，作主语，动词宾语或介词宾语。如：
This is the reference book which you want.
这就是你要的那本参考书。
The building which stands near the river is our school.河边的那所建筑物是我们学校。
下面几种情况通常用which，不用that。
（l）关系代词在介词后面时。如：
This is the chair on which I sat just now.。
这就是我刚才坐的那把椅子。
That is the house in which we lived last year.
那就是去年我们住的房子。
如果要用that引导定语从句，则介词不能放在前面，只能放在从句中相关动词的后面。在含有介词的固定短语动词中，介词不能提前。 |
（2）在非限定性定语从句中。如：
They are hollow, which makes them very light.．
它们是空的，这使得它们很轻。
The book,which was written in 1994, was published in 1996.
1994年写的那本书，1996年才出版。
（3）先行词为that时。如：
What's that which you are looking at?
你们正在看什么？
What's that which you are holding in your hands?你手里拿的什么？
3．who,whom,whose
who，whom指人，在从句中作主语、宾语。whose既可指人，也可指物，在从句中作定语。
如：
The professor who comes from Beijing University is famous.．
从北京大学来的那位教授是很著名的。
The writer whom we met in the street gave us a lecture last month.我们在街上碰到的那位作家上个月给我们作过一次报告。
The bike whose bell doesn't work is mine.
那辆铃不响的车子是我的。
4.as
（l）as作代词，引导定语从句，主要用于the same as ,the same…as或such…as 结构中，这时as 相当于who或which。如：
The house is just the same as it used to be.
这所房子和过去没什么差别。
Such people as you are talking about will surely succeed.你说的这种人肯定会成功的。
（2）引导非限定性定语从句时，它指的是主句所表达的整个内容。这种从句表示谈话人对谈话内容的看法或态度，可以放在句首，句中或句末。如：
Mike,as you know, is a good man.
如你所知，迈克是个好人。
The elephant is like a snak，as anybody can see.任何人都能看到，大象像条蛇。
which和as引导非限定性定语从句的区
别。
Which引导非限定性定语从句：
（l）只代替主句的部分内容。
（2）可代替主句的全部内容。
（3）代替主句中表物或事的一个名词或词组，且对其进行说明。
（4）当定语从句为复合结构，且关系词为宾语时。
（5）定语从句为否定句时。
（6）定语从句为主动句，且关系词在从句中作主语时。
as引导非限定性定语从句。
（l）可放在主句前，也可放在主句后。
（2）表达“正如，就像”意义时。
（3）从句谓语为know,explain, say, expect, imagine, show, report, announce, point out时。
（4）在从句中作表语，且只代替主句的表语时。
另外，当从句内容对主句内容有消极作用或含义不一致时，常用which引导非限定性定语从句；如果语意一致，则常用as引导非限定性定语从句。
5．when, where, why
when，where，why分别表示时间、地点和原因，在从句中作时间状语、地点状语和原因状语。如：
I will nevre forget the day when I joined the Party.我永远不会忘记我入党的那一天。
One morning an elephant was led down the road where they stood.一天早晨，一头大象从他们所站的那条路上被赶过去。
We don`t know the reason why they didn't complete their production plan according to the schedule.我们不知道他们为什么没有按计划完成生产计划。
Do you still remember the days______ we worked together?
Do you still remember the days______ we spent together?
Do you still remember the place______ my mother once worked?
Do you still remember the place______ we visited that year?
Do you still remember the place______ we spent our holidays?
能否用when和where引导定语从句，需要判断从句谓语动词是及物动词还是不及物动词。如果从句谓语动词为不及物动词，用when和where引导定语从句，它们分别在定语从句中作时间状语和地点状语。如果谓语动词为及物动词，用which或that引导定语从句，在从句中作宾语。 |
6．关系代词whom, which在定语从句中作介词宾语时，介词一般放在whom,which之前。介词由两方面来确定。
（l）根据动词和介词的搭配来确定。如：
This is the house in which we lived last year．
这就是我们去年住的房子。
There comes the man about whom we just talked.我们刚才谈论的那个人过来了。
（2）根据从句的意思来确定。如：
He built a telescope through which he could study the skies.他建造了一个望远镜，通过这个望远镜他就能观察天体。
Wei Hua，with whom I palyed pingpong yesterday, is not here now.和我昨天一起打乒乓球的魏华现在不在这儿。
7．定语从句的两个特殊句型
（l）Is this school we visited that year?
Is the school we visited that year?
Is this the school we visited that year?这就是我们那年参观过的那所学校吗？
前两个句子无先行词，应先加上先行词the one。第三个句子用that引导定语从句，因为the school在主句中作表语，先行词为表语时，用that引导定语从句。并且从句谓语为及物动词，不能用where。
（2）He is one of the students who are from the south.他是从南方来的学生之一。
He is the only one of the students（the only
student） who is from the south．
他是唯一的一个从南方来的学生。
第一句中先行词为 the students，定语从句的谓语动词用复数。第二句中先行词为theonly one，所以定语从句的谓语动词用单数。
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