定语从句中常用的关系副词有：when，where，why，在定语从句中分别作时间状语，地点状语和原因状语。
1.when的用法
when代替的先行词是表示时间的名词，在定语从句中作时间状语。when往往可以由介词+which代替。
Can you tell me the time when the film will start? 你能告诉我电影什么时候开始吗?
Can you tell me the time at which the film will start?
The solution to the mystery of the monarch’s amazing ability comes at a time when it is in serious trouble. 金斑蝶惊人能力之谜的谜底在它陷入严重困境之际揭晓。（新外研版必修一）
（when可以用during which代替）
2.where的用法
where代替的先行词是表地点的名词，在定语从句中作地点状语。where往往可以由介词+which代替。
Eventually, it manages to reach the places where it will spend the winter. 最终，它设法到达了过冬的地方。（新外研版必修一）（where可以由in which代替）They were welcomed to the Chinese-style compound where they were to live. 他们受到了欢迎，住在中国式的大院里。（新外研版必修一）（where可以由in which代替）
where的先行词也可以是一些类似于地点的抽象名词，例如，case（情况，案例），situation（情况，形势，境遇），degree（程度），point（时刻，阶段），job（工作），career（事业），family（家庭）等。
We have reached a point where a change is really needed. 我们已经到了一个真正需要改变的时刻。
I don’t want a job where I’m always ordered to do the work all day. 我不想要一份总是被命令整天干活的工作。
We have got into a situation where we were supposed to make a decision immediately. 我们陷入了一种应该立即做出决定的境地。
All the neighbors admire this family where the parents are treating their child like a friend. 所有的邻居都很羡慕这个家庭，他们的父母像对待朋友一样对待他们的孩子。
