介词＋which ／whom的用法
1．语法作用：“介词＋关系代词”在从句中主要起关系副词的作用，即在定语从句中充当状语：
（1）表示地点，时间和原因的“介词＋which”分别相当于 where，when，why。
I have found the book in which the names of all the early satellites are mentioned．（＝I have found the book．The names of all the early satellites are mentioned in it．）
The earth on which ／where we live is a planet．
I'll never forget the day on which ／when I joined the League．
I know a wood in which ／where you can find roses．
Is there any reason for which ／why you should have a holiday？
（2）way后常用that代替in which，也可省略that。
I really don't like the way that he talks．
That was the way in which the old lady looked after us．
Do it the way I showed you．
2．“of ＋which”起形容词的作用，相当于whose（用来指物），其词序通常是“n．＋of which”。
They live in a house whose door ／the door of which opens to the south．
He's written a book whose name ／the name of which I've com- pletely forgotten．
3．可引导限制性定语从句和非限制性定语从句
There is a rocket by which the direction of the satellite can be changed．
We carefully studied the photos，in which we could see signs of plant disease．
4．介词的选择（选择介词时须考虑下列情况）
1）介词与先行词的习惯搭配
There is no way in which it could be brought back to the earth．（in与way是习惯搭配）
2）介词与定语从句中的动词，形容词的习惯搭配
These are the wires with which different machines are connected．（be connected with是习惯搭配）
The author with whom all of us are familiar will visit our compa-ny．（be familiar with是习惯搭配）
3）同形的先行词，或定语从句中的动词，形容词表示不同的含义时，要根据其含义选用不同的介词。
I can't remember the age at which he won the prize．
That is the age in which people live in peace and happiness．
age在前句中意为“年岁”，与at搭配；在后句中意为“时期”，与 in搭配。
4）复杂介词须保持其完整形式，常见的复杂介词有on the top of，in the middle of，in front of，in spite of，at the back of，because of等。
We took a photo of rocket，the length of which was about 30me- tres.
Sound is a tool by means of which people communicate with each other．
They marched through the square，in the middle of which stood a monument．
5）短语动词中的介词不可与动词分开提至关系代词前。常见的短语动词有listen to，look at，depend on，pay attention to，take care of，look into，break into，get rid of，take part in，make use of，take hold of，catch hold of，catch up with，get along with，look forward to等。此时可用which，who，whom或that，也可将他们省略。
（误）This is the girl of whom he will take care．
（正）This is the girl whom he will take careof．
6）当介词与定语从句中的动词或形容词联系紧密（但不是短语动词）时，介词也可放在动词或形容词的后面。但当介词与从句中的动词或形容词联系不紧密时，则需将介词置于关系代词前。比较：
The space station which we drove to was in the desert．
I'll never forget the day in which I joined the Party．
后句中若置于句尾则有“孤零零”之感，这时宜将介词置于关系代词前；而前句中的to则可后置。
5．关系代词的选择
用于介词后的关系代词只有which，whom，前者指物，后者指人。
There are many research stations on the earth in which outer space is studied.（which指代research stations）
We questioned the pilot，from whom we learnt that no other planes had been seen．（whom指代the pilot）
来自:
http://hi.baidu.com/gaohongwei83/blog/item/d1d96a1084d90df8c2ce7946.html