一、“介词+关系代词”结构
1. 可代替when, where, why, that等关系词
e.g. There is no reason for which (why) we shouldn’t be friends.
2. 介词后面的关系词不能省略。
e.g. Here is the money with which to buy a piano.
3. that前不能有介词。
4. 某些在从句中充当时间，地点或原因状语的“介词+关系词”结构可以跟关系副词when 和where 互换。
e.g. This is the house in which I lived two years ago.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?
Do you remember the day when you joined our club?
