介词加关系代词引导的定语从句主要用于正式文体。直接用于介词后作宾语的关系代词which不能换成that，直接用于介词后作宾语的关系代词whom不能换成who。
“介词+关系代词”引导定语从句
1.由“介词+关系代词”引导的定语从句主要用于正式文体，在非正式文体中通常将介词放至句末。
如：This is the man to whom I referred.我指的就是这个人。
This is the man (whom) I referred to.我指的就是这个人。
2.直接用于介词后作宾语的关系代词which不能换成that，直接用于介词后作宾语的关系代词whom不能换成who。但若介词用于句末，则用作宾语的which,whom也可换成that,who，或者省略。
如：这是一个我们讨论了许多的问题。This is a subject about which we have talked a lot.(which不能换成that，也不能省略)
This is a subject which we have talked about a lot.这是一个我们讨论了许多的问题。(which可以换成that，也可以省略)
3.关系副词when,where,why根据情况有时可换成“介词+关系代词which”。
如：That is the day when[=on which]he was born.那就是他出生的日子。
That is the house where[=in which]he lived.那就是他住过的房子。
That is the reason why[=for which]he must apologize.那就是他必须道歉的原因。
4.在很正式的文体中，“介词+关系代词”引导的定语从句可紧缩成“介词+关系代词+不定式”结构。如：在那儿孩子们有个玩耍的花园。正：There the children had a garden in which to play.(很正式)
正：There the children had a garden in which they could play.(较正式)
正：There the children had a garden to play in.(较口语化)
注：这类“介词+关系代词+不定式”结构中的介词不能没有，也不能放在句末。如不能说There the children had a garden which to play in.
“介词+关系代词”的结构
1.“介词+ which”在关系分句中分别可作时间、地点和原因状语，代替相应的关系副词when, where和why。如：
①I still remember the day on which (=when) I first came to school.我仍然记得初来学校的那一天。
②The factory in which (= where) I work is a large one.我工作的工厂是一个大厂子。
2.“介词+ which（指物）/whom（指人）”在关系分句中作地点状语，表示存在关系，关系分句主谓常须倒装。如：
①They arrived at a farm house, in front of which sat a small boy.他们来到一处农舍，前边坐着一个小男孩。
②I saw a man, on the head of whom stood a bird.我看见一个人，他的头上有一只鸟。
3.“不定代词或数词+ of + which（指物）/whom（指人）”在关系分句中作主语，说明整体中的一部分。如：
①China has a lot of islands, one of which is Diaoyu.中国有许多岛屿，其中之一是钓鱼岛。
②There are a lot of students here, none of whom like the film.这里有许多学生，他们之中无人喜欢这部电影。p分页标题e
4.“介词+ which（指物）/whom（指人）”在关系分句中作目的、方式或地点状语。如：
①Could you tell me for whom you’ve bought this coat? 你能告诉我这件衣服是给谁买的吗？
②The man, from whom I learned the news,is an engineer.这人是一位工程师，我是从他那里得到这个消息的。
5.“介词+ which（指物）/whom（指人）”用于被动结构的关系分句中，作状语，说明动作的执行者。如：
①The wolf by which the sheep was killed was shot.伤害羊的那只狼被打死了。
②The man by whom the wolf was shot was a good hunter.打死狼的那人是一个好猎手。
6.“名词+of which”代替“whose+名词”在关系分句中作定语。如：
①I saw some trees,the leaves of which (= whose leaves ) were black with disease.我看见一些树，它们的叶子因害病而发黑。
②He mentioned a book, the title of which (= whose title) I’ve forgotten.他提到一本书，书名我忘了。
7.“介词+which（指物）/whose（指人）”修饰后边的名词。如：
①It rained all night and all day, during which time the ship broke into pieces.雨下了一天一夜，就在这期间轮船撞碎了。
②The driver was the man from whose room she had stolen the maps.司机就是那个男人，她从他的房间偷走地图。
8.“介词+which+不定式”。此种用法多见于正文体中，相当于一个带有主语和谓语的定语从句。如：
She had only 1.87 with which to buy (=she could buy) Jim,her husband,a present.她只有一元八角七分钱，用这些钱她给丈夫吉姆买一件礼物。
