1.关系副词when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)

　　2.关系副词where的用法

　　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。

　　3.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？