关系副词有when, where, why ，在定语从句中作状语，分别表示时间、地点和原因。when的先行词通常是表示时间的名词；where的先行词通常是表示地点或情形的名词；why的先行词只能是reason 。关系副词when和where有时可用"介词+ which"代替，why可用for which代替。如：
There are occasions when ( = on which) one must yield.
Beijing is the place where ( = in which) I was born.
Is this the reason why ( = for which) he refused our offer?
1. The factory where his father worked has closed.
比较：The factory which/that was built in 1978 has closed.
2.I'll never forget the days when we lived together.
比较：1,11 never forget the days (that) we spent in Australia.
3. The reason (why) she was ill was that she had eaten bad meat.
比较：The reason (that) he gave for his absence was obviously fabricated.