1. 关系代词：主要有that, which, who, whom, whose, as等，它们在句子中可用作主语（如that, which, who等）、宾语（如that, which, whom等）和定语（如which, whose）。如：
Is he the man that sells dogs? 他就是卖狗的人吗? She is the girl who won the prize. 她就是获奖的姑娘。
I’ve found the book which I was looking for. 我找到了我要找的书。 She is the woman whose car was stolen. 她就是汽车被盗的那个女人。 She is the woman whom I gave the money to. 她就是我给她钱的那位妇女。
He is absorbed in work, as he often was. 他正在全神贯注地工作，他过去经常这样。 2. 关系副词：主要有where, when, why等，它们在句子中主要用作状语。如： This is the town where I was born. 这就是我出生的城市。
I’ll never forget the day when I first met you. 我永远不会忘记第一次见你的那天。 We don’t know the reason why he didn’t show up. 我们不知道他为什么没有来。
关系代词who, whom, whose 用法说明
■ 关系代词who, whom)的用法
who和whom均只用于指人，不用于指事或物，其中who在定语从句中用作主语，whom在定语从句中用作宾语。如：
I met a girl who knew your sister. 我碰到一个认识你姐姐的姑娘。
In Berlin, he first met the woman whom he would one day marry. 在柏林，他第一次遇见那个女人，后来他终于跟她结了婚。
She introduced me to her husband, whom I hadn’t met before. 她把我介绍给她丈夫，我以前没见过他。
但是，用作宾语的whom如果不是紧跟在介词之后，通常会被省略或用who, that代之。如：
The person to whom I complained is the manager. 我向他投诉的那个人是经理。 The person (who, whom, that) I complained to is the manager. 我向他投诉的那个人是经理。
■ 关系代词whose的用法
关系代词whose既可用于指人，也可用于指事或物，它在定语从句中主要用作定语。如： She is the woman whose car was stolen. 她就是汽车被盗的那个女人。 This is the house whose windows were broken. 这就是窗户被打破了的房子。
Mrs. Gray, whose children are in college, is trying to get a job. 格雷太太的孩子们都在上大学，她想找一份工作。
His house, whose windows were all broken, was a depressing sight. 他的房子窗户无一完好，一派令人心酸的景象。
关系代词which重要用法说明
■关系代词which只用于指事或物，不用于指人，它在定语从句中主要用作主语或宾语。如：
She was not on the train which arrived just now. 她不在刚才到达的那列火车上。(关系代词which指train，在从句中用作主语)
He never got back the money which he had lent him. 他从未收回他曾借给他的那笔钱。(关系代词which指money，在从句中用作宾语)
■which用于引导限制性定语从句外，还可以引导非限制定语从句。如：
The ship struck an iceberg, which tore a huge hole in her side. 船碰在一座冰山上，船帮被撞出一个大洞。
She gave me this jumper, which she had knitted herself. 她送给我这件羊毛衫，这是她亲手织的。
This machine, which I have looked after for twenty years, is still working perfectly. 这台机器我已经照管了20年，现在仍然没一点儿毛病。
■which有时也可用作定语，尤其用于“介词+which+名词”这类结构中，此时的which含有this或that的意味。如：
He may be busy, in which case I’ll call later. 他可能忙，如若如此，我以后再来拜访。 I may have to work late, in which case I’ll telephone. 我可能得晚点下班，那样我会打电话的。
He lost his temper, at which point I decided to go home. 他发脾气了，这时我就决定回家了。
He was appointed Lord Chancellor, in which post he spent the rest of his life. 他被任命为大法官，在这个职位上度过了他的后半生。
The postman comes at 6.30 in the morning, at which time I am usually fast asleep. 邮递员早晨6点30分来，这个时候我通常还睡着大觉呢。
It was derived from Posidonius, for which reason much of its information may well have been out of date. 它源于鲍森杜尼尔斯。由于这个原因，它的大部分信息很可能已经过时。
有时其前也可以没有介词。如：
He is studying economics, which knoweledge is very important today. 他学经济学，这种知识现今很重要。
He spoke in Greek, which language I could only follow with difficulty. 他说希腊语，我听起来很吃力。
■ 关系代词which有时可用于指人。原则上说，which用于指事物，不用于指人。但
以下情况属于例外：
1. 用于在指人的名词之后，指不强调性别的婴儿：
He was the last child which was born. 他是最后出生的孩子。(which指小孩)
2. 当不是指具体的某人，而是指人的属性（如职业、身份、地位、职务、品质、特征等）时，则也用关系代词 which而不用 who。如：
They accused him of being a traitor, which he was. 他们指控他是叛徒，他真是叛徒。 She talked like a native, which she hardly was. 她说起话来像是个本地人，其实她不见得是。
■ 在非常正式的文体中，代词that后可以接一个修饰它的定语从句，这个定语从句通常用which来引导。如：
They say the only real knowledge is that which can be measured. 据说唯一真实的知识是可以检验的知识。
在现代英语中，that which通常用what来代替。如：
We have that which (=what) we need. 我们需要的东西都有了。
That which (=What) many people say is not always true. 很多人说的话并不表示一定是真的。
关系代词that用法归纳
一、指人的用法
that用于指人，在定语从句中可用作主语、宾语或表语。如：
A driver that has knocked someone down must stop. 撞人的司机必须停车。(关系代词that指driver，在从句中作主语)
He is the man that you have been looking for. 他就是你要找的那个人。(关系代词that指man，在从句中作宾语)
He is not that man that he was. 他已不是过去的他了。(关系代词that指man，在从句中作表语)
二、指物的用法
that用于指物，在定语从句中可用作主语、宾语或表语。如：
This is the plane that will fly to Tokyo in the afternoon. 这是下午要飞往东京的那架飞机。(关系代词that指plane，在定语从句中作主语)
She was annoyed by something that I had said. 她为我说的某句话而不高兴。(关系代词that指something，在定语从句中作宾语)
Shengzhen is not the city that it used to be. 深圳现在已不是原来的那个城市了。(关系代词that指city，在定语从句中作表语)
有朋友问到 from which与from where 有何区别（问题见：
http://www.yygrammar.com/GuestBook/Guest_Reply.asp?TopicID=479），下面是我们的一位特约作者给出的部分回答，摘录如下，供大家参考：
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关于from which的用法比较好理解，这里主要说说from where的用法。from where主要有以下两个用法：
用法一：用于引导非限制性定语从句，在意义上相当于 and from there（从那儿）。如： He hid himself in a tree, from where he could see the enemy in the distance. 他躲在一棵树上，从那儿他可以看到远处的敌人。
We went up to the roof, from where we had a good view of the procession. 我们爬上屋顶，从那儿可以很好地观看游行。
用法二：可视为where前省略了the place，即这样用的from where 相当于from the place where，意思是“从??的地方”“离??的地方”。如：
From where I stood I could see everything clearly. 从我站的地方我一切都看得清清楚楚。 The car stopped short only a few inches from where I stood. 汽车在离我站的地方仅几英寸处突然停住。
from which与from where的区别
The school was only a few blocks from where she lived. 学校离她的住所只有几个街区的距离。
若遇到前面是地点名词的先行词，如何判断用where还是from where还是from which?请看下面一个句子：
I have bought that house, _____I can enjoy the beautiful scene of Yangpu Bridge .
我们认为这道题填 where 和 from where 语法上都可以（但不宜填 from which），但两者在意义上稍有区别：
I have bought that house, where I can enjoy the beautiful scene of Yangpu Bridge. 我买下了那栋房子，在房子那可以欣赏到杨浦大桥的美景。
I have bought that house, from where I can enjoy the beautiful scene of Yangpu Bridge. 我买下了那栋房子，从房子那可以欣赏到杨浦大桥的美景。
在许多情况下，用不用 from 不会导致语法错误，但会导致语义变化（通常情况下是，如果没有 from，意思会不够明确和清楚）。比较：
He hid himself under the bed, from where he could hear what they were talking. 他躲在床下面，他可以从床下听到他们谈话。（句中的 from where 可理解为 from under the bed，意思是“从床下面”）
He hid himself under the bed, where he could hear what they were talking. 他躲在床下面，在床那儿他听到他们谈话。（句中的 where 可指为“在床边”“在床上”“在床下”等，意思不够明确）
如何使用“介词+关系代词”结构
对于“介词+关系代词”结构的使用，重点是要弄清其中的介词如何确定和判断。归纳起来，有以下几点方法：
1. 根据与定语从句中动词的搭配来确定介词。如：
Water is the natural medium in which fish live. 水是鱼类赖以生存的自然环境。(注意搭配live in)
The documents for which they were searching have been recovered. 他们找寻的文件已经找到了。(注意搭配search for)
This is a subject about which we might argue for a long while. 这是一个我们可能长时间争论的问题。(注意搭配argue about)