一、基本概念 
关系副词的意思相当于“介词+which结构”，在定语从句中做状语的成分。
1.He will always remember the day when/on which his father returned from America.
他将永远记得父亲从美国返回的那一天
拆分后：
He will always remember the day.
His father returned from America on the day..
 
2.This was the time when/at which she left for Beijing.
这就是她动身去北京的时间。
拆分后
This was the time.
She left for beijing at the time.
 
3.I don’t know the reason why/for which he didn’t come to the meeting yesterday morning.
我不知道他为什么没有参加昨天上午的会议。
I don’t know the reason.
He didn’t come to the meeting yesterday morning for the reason. 
重要提示：
在when、where、why关系副词引导的英语定语从句中，只会出现when、where、why或on which、at which、for which等等，绝对不会出现on when、at where、for why这种情况，因为关系副词引导的定语从句只能起状语作用，既不能做动词的宾语，也不能做介词的宾语。