定语从句中关系副词的用法
when 既可引导限制性定语从句，又可引导非限制性定语从句。先行词是时间名词，在从句中充当时间状语，相当于“介词+which”。如：
Can you tell me the time when the film will start?—Can you tell me the time at which the film will start? 请告诉我电影什么时候开始好吗？(限制性定语从句)
I will never forget the day, when I joined the Party. —I will never forget the day, on which I joined the Party. 我入党的那一天，我永远不会忘记。(非限制性定语从句)
where既可引导限制性定语从句，又可引导非限制性定语从句。先行词是地点名词，在从句中充当地点状语，相当于：“介词+which”。如：
This is the school where I studied a few years ago. —This is the school in which I studied a few years ago. 这就是我几年前所在读书的学校。
Let’s go to the concert, where you will find much fun. —Let’s go to the concert, in which you will find much fun. 我们去音乐演唱会吧，在那里你会找到很大的乐趣。
■关系副词why的用法
why只能引导限制性定语从句，先行词只有reason一词，在从句中充当原因状语，相当于：“for + which”。如：
Do you know the reason why he is not here now?—Do you know the reason for which he is not here now? 你知道他还没有来这儿的原因吗？
■关系副词that的用法
that只能引导限制性定语从句，充当关系副词时，其作用相当于：“介词+关系代词”，在从句中充当时间、地点、方式、原因状语等。如：
1. 在定语从句中作时间状语。现行词有：each time, every time, anytime, the first time, the moment, the minute, the hour, etc. 但现代英语中，that往往省略。如：
Each time (that) I meet him, he will smile and say “hello”. 每次我会见他时，他都会笑着说“喂，你好!”
2. 在定语从句中作方式状语, 现行词是way, 如：
Can you show me the way (that) you solve the problem like this? 请告诉我你解决这类问题的方法好吗？
3. 在定语从句中作原因状语，现行词只有reason一词，如：
I don’t know the reason (that) he has left school now. 我不知道他辍学的原因。
4. 在定语从句中做其他状语，现行词如price, speed等，如：
I think the price (that) she sells her apple is too high. (that = at which) 我认为她卖苹果的价格太高。
。