1）The 3 yuan for which I bought the book was borrowed from my friend.

　　2）Smith，from whom we've learned a great deal，is an old worker.

　　根据先行词与介词的某种习惯搭配。如：

　　His bag，in which she put all her books，has not been found.

　　根据从句中动词与先行词的逻辑关系。如：

　　1）This colorless gas is called oxygen，without which we could not live.

　　2）This colorless gas is called oxygen，with which we can rescue patients.

　　3.定语从句中介词的位置：

　　在书面语中，介词多放在关系代词之前，口语中多放在后面。如：

　　1）This is the man to whom you spoke.（书面语）

　　2）This is the man who/whom you spoke to.（口语）

　　在限制性定语从句中，介词可放在关系代词之前或之后；在非限制性定语从句中，介词一般放在关系代词之前。

　　介词如果是定语从句中短语动词的固定部分，要放在动词之后，多半不拆开用。如：

　　Is this the book which he was looking for?（不可将for放在which之前）

　　如果介词是由句中先行词决定的，还是放在关系代词之前为好。如：

　　The speed at which light travels is 300 000 km per second.

　　"介词+关系代词"作定语时，介词不能后置。如：

　　I live in a room，the window of which opens to the south.

　　当介词位于定语从句的末尾时，可用that替代which 或whom,也可用who替代whom。且常省略关系代词。如：

　　1）This is the pen(that/which) he wrote the letter with.

　　2）The doctor(that/who/whom) she sent her friend to is very well known.

　　4.whose 可转换为"of+关系代词"的结构。如：

　　They live in a house whose door opens to the south.

　　→They live in a house of which the door opens to the south.

　　→They live in a house the door of which opens to the south.

　　5.关系副词when,where,why和"介词+which"可相互代替。如：

　　when=in/on/at...+which,where=in/on/at...+which,why=for which。

　　1）I won't forget the date when(=on which) I was born.

　　2）This is the room where(=in which) I lived.

　　3）I don't know the reason why(=for which) he hasn't come today.