爱华网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 thenames of all the early satellites are mentioned．（SEFC 2A L．55）（＝Ihave found the book．The names of all the early satellites arementioned in it．）
The earth on which ／where we live is aplanet．
I'll never forget the day on which／when I joined the League．
I know a wood in which ／where you canfind roses．
Is there any reason for which ／why youshould 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 hetalks．
That was the way in which the old ladylooked 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 ／thedoor of which opens to the south．
He's written a book whose name ／thename 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 whi ch thedirection of the satellite can be changed．（SEFC 2A L．55）
We carefully studied the photos，inwhich we could see signs of plant disease．（SEFC 2A L．55）
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 bebrought back to the earth．（SEFC 2A L．55）（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 whichdifferent machines are connected．（be connected with是习惯搭配）
The author with whom all of us arefamiliar 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 hewon the prize．
That is the age in which people live inpeace 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，inthe middle of，in front of，in spite of，at the back of，becauseof等。
We took a photo of rocket，the length ofwhich was about 30me- tres．（SEFC 2A L．55）
Sound is a tool by means of whichpeople communicate with each other．
They marched through the square，in themiddle 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listento，look at，depend on，pay attention to，take care of，look into，breakinto，get rid of，take part in，make use of，take hold of，catch holdof，catch up with，get along with，look forwardto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 willtake care．
（正）This is the girl whom he will takecareof．
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 wasin the desert．（SEFC 2A L．55）
I'll never forget the day in which Ijoined 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 theearth in which outer space is studied．（SEFC 2AL．55）（which指代research stations）
We questioned the pilot，from whom welearnt that no other planes had been seen．（SEFC 2A L．55）（whom指代thepilot）
