在定语从句中，当关系副词引导定语从句时，关系副词可以换为“介词加which”.
例句：
1.This is the house where Tom lived many years ago.
把关系副词where换为“介词加which”
This is the house in which Tom lived many years ago.
2.This is the reason why he was late for the meeting.
把关系副词why换为“介词加which”
This is the reason for which he was late for the meeting.
时间先行词后面介词加which相当于when,地点先行词后面介词加which相当于where,for which相当于why。
