1）介词后面的关系词不能省略。
2）that前不能有介词。
3） 某些在从句中充当时间，地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换。
　 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 club¹?
　 Do you remember the day when you joined our club?

上一篇：限制性和非限制性定语从句 下一篇：as, which 非限定性定语从句