[观察例句]
1．There are occasions when one must yield.
2．Beijing is the place where I was born.
3．Is this the reason why he refused our offer?
[归纳用法]
当先行词在定语从句中作状语时，通常要用关系副词引导定语从句。常用的关系副词有when，where和why。
一、关系副词when
1．when引导的定语从句的先行词往往是表示时间的名词，如time，day，hour，month，year，在从句中作时间状语。
2．when既可以引导限制性定语从句，又可以引导非限制性定语从句。
3．关系副词when常可用“介词＋which”来代替。
I'll never forget the days when we stayed in the countryside.我永远忘不了我们在乡下待过的日子。
(when引导限制性定语从句，可用 on which代替)
Do you still remember the time when we met our old friend John?
你还记得我们遇见我们的老朋友约翰的时候吗？
(when引导限制性定语从句，可用 at which 代替)
In the old days，when our country was not so strong，peasants lived a hard life.
在过去，我们的国家还没有这么富强的时候，农民们过着苦日子。
(when引导非限制性定语从句，可用in which 代替)
[即时训练1]
①Between the two parts of the concert is an interval，when the audience can buy icecream.
②The days are gone when physical strength was all you needed to make a living.
