[语法点津]
一、基本用法
当关系代词在定语从句中充当介词的宾语时，我们用介词＋关系代词(whom或which)引导定语从句。如果指人，用介词＋whom；如果指物，用介词＋which。介词前置时，关系代词不能用that或who，即介词不与that或who连用。若介词后置则可以用that/who，还可省略。
Do you know the boy to whom she was talking?
你知道与她交谈的那个男孩是谁吗？
The little girl is reading a book in which there are many pictures.
那个小女孩正在读一本书，书中有很多图画。
Have you found the book from which we learnt a lot?
你找到那本我们从中学了很多的书了吗？
二、介词的选择
1．根据定语从句中的谓语动词或形容词确定介词。该动词或形容词与介词搭配，构成动词短语或形容词短语。
①Is this the car for which you paid a high price?
这是你花大价钱买的车吗？(for和pay搭配)
②This is the house in which I lived two years ago.
这是我两年前住过的房子。(in和live搭配)
2．根据先行词与介词的搭配习惯来确定。
I'll never forget the day on which I joined the army.
我永远也忘不了我参军的那一天。(具体到某一天，用介词on)
She never explained the reason for which she was late for the class again.
她没有解释她再一次上课迟到的原因。(the reason for为固定搭配，意为“……的原因”)
3．根据句子的意思确定介词。有些句子，先行词完全一样，定语从句中谓语动词也不是固定的动词短语。这时，需要根据句子所要表达的意思选用不同的介词。
He broke his glasses，without which he can't see anything.他打破了眼镜，没有眼镜他什么也看不见。
This is the pilot by whom my son was saved.(My son was saved by the pilot.)
这就是救了我儿子的那位飞行员。
三、介词＋关系代词需注意的问题
1．关系副词(when，where，why)常可转换为“介词＋which”的形式
关系副词why，when，where在句中作状语时，可用“介词＋which”替换：why＝for＋which，when＝at/on/in/...＋which，where＝at/on/in...＋which。
I'll never forget the days when(in which/during which) I worked with you.
我将永远不会忘记和你一起工作的那些日子。
This is the office where (in which)I used to work.
这就是我过去工作过的办公室。
I'd like you to explain the reason why (for which) you were absent.
我想让你解释一下你缺席的原因。
2．关系代词whose可转换为“介词＋which/whom”，“whose＋名词”可与“the＋名词＋of which/whom”或“of which/whom＋the＋名词”互换
The book，the cover of which/whose cover is red，is written by Mr.Jones.
这本书是琼斯先生写的，它的封面是红色的。
He lives in the room，the window of which/whose window faces south.
他住在那屋子里，它的窗子朝南。
3．在表示部分与整体的关系时，常在of which/whom 前加一些表示部分或整体的词语
some of which/whom，one of which/whom，数字＋of which/whom等。
He has two sons，both of whom work as actors.
他有两个儿子，都是演员。
He kept ten dogs，eight of which were over five years old.
他养了十条狗，其中八条五岁以上了。
4．含有介词的短语动词一般不能拆开，如look after，be made of，take part in，look forward to等。
Is this the book (which/that) you are looking for?
这是你在找的书吗？
The babies(who/whom)the nurses look after look strong and happy.
护士们照看的孩子们看起来很壮，很幸福。
