“介词＋关系代词”引导的定语从句在英语中很常见，它既可以引导限制性定语从句，也可以引导非限制性定语从句。虽然其中的关系代词常用的只有 which和whom，但其扩展形式却很多。归纳起来有以下几种：
1、“介词＋关系代词”结构
这是最普遍的结构，其中介词是从句本身的结构或其中动词搭配所要求的。例如：
The goals for which he had fought all his life no longer seemed important to him．他终生奋斗的目标对他似乎不再重要了。
The tower of London，in which so many people lost their lives is now a tourist attraction．伦敦塔，这个以前多少人在此丧命的地方，现在已成了旅游胜地。
用于这个结构中的介词，既可以是单个的介词，也可以是短语介词，如ac- cording to，because of，by virtue of，by means of，in spite of等。例如：
In order to prevent overloading a circuit，we use a protective device，by means of which the circuit is broken at once in case it is overloaded．为了防止电路过载，我们采取防护装置，借助这种装置，在过载的情况下电路会立刻断开。
有时，“介词＋关系代词”在意义上相当于where，when，why这类关系副词。例如：
I revisited the place in which I GREw up．（＝I revisited the place where I grew up．）我重访了我成长的那个地方。
1974was the year in which I was born．（＝1974was the year when I was born．）我出生在1974年。
2、“代词＋介词＋关系代词”结构
用于这个结构中的代词主要是 both，all，much，many，（a）few，（a）little，none，some，several，most等不定代词，而其后的介词多用of。例如：
There are many books on the table， some of which are Professor Black's．桌子上有许多书，其中有些是布莱克教授的。
The body is made of a large number of organs，each of which has its particular function．身体由许多器官构成，各个器官都有独特的功能。
We have nearly one hundred foreign students in our university，most of whom are from America and Australia．我们大学有近一百个留学生，其中大部分来自美国和澳大利亚。
3、“名词＋介词＋关系代词”结构
这个结构在引出的定语从句中作主语时，要注意谓语动词数的问题，分清关系代词所代表的先行词与介词前各成分数量的关系或性质。例如：
A survey was carried out on the death rate of new-born babies in that region，the results of which were surprising．曾经对那个地区新生儿死亡率进行过调查，其结果令人吃惊。
Molecules make up matter，the state of which can be changed by the increase and decrease of its temperature．分子组成物质，物质的状态可以由温度增减而改变。
这种结构中“介词＋关系代词”所构成的介词短语修饰前面的名词。因此，名词也可以放在关系代词之后。例如：
A compass has a needle，the ends of which always point north and south．（＝A compass has a needle，of which the ends always point north and south．）指南针有根指针，它的两端总是指向南北。
4、“数词＋介词＋关系代词”结构
There are many forms of energy，one of which is atomic energy．能量有许多种形式，原子能就是其中的一种。
This device consists of over 2000
parts，two-thirds of which are made of plastics．这个装置有2000多个部件，三分之二是塑料的。
The house was full of children，ten of whom were that old man's own grandsons．屋子里满是孩子，其中十个是那个老人自己的孙子。
5、“形容词＋介词＋关系代词”结构
其中形容词多用比较级或最高级形式，因为形容词前有定冠词the，实际上这个形容词相当于名词。例如：
There are different kinds of liquid solvents，the most important of which is water．液体溶剂种类繁多，其中最主要的是水。
Our university has many laboratories， the largest of which was built last year．我们学校有许多实验室，其中最大的是去年建造的。
There are many big rivers in the world，the second longest of which is the Nile River in Africa．世界上有很多大河，第二长的是非洲的尼罗河。
5、“介词＋whose ＋名词”结构
whose代表先行词的所有格引出定语从句，“whose ＋名词”在从句中作介词的宾语，whose作名词的定语。例如：
The families at whose house we stayed are friends of my father's．我们曾在他们家住过的那家人是我父亲的朋友。
Mr．Brown is a man on whose words you may rely．布朗先生是一位可以信得过的人。
