一、基本用法
    when 表示时间，where 表示地点，why 表示原因。如：
    There came a day when the rain fell in torrents. 有一天下着倾盆大雨。
    July and August are the months when the weather is hot. 七八月是天气很热的月份。
    That's the hotel where we were staying last summer. 这就是我们去年夏天住的旅馆。
    He rents a room near the office where he works. 他在他工作的办公室附近租了一间屋子。
    Do you know the reason why I left early? 你知道我为什么早走吗?
    The main reason why he lost his job was that he drank. 他失去工作的主要原因是他喝酒。
    用法延伸：关系副词有时可换成“介词＋which”。如：
    I’ll never forget the day when [on which] we first met. 我永远不会忘记我们第一次见面的那一天。
    That’s the house where [in which] he lived 10 years ago. 那就是他10年前住过的房子。
    That’s the reason why [for which] he came. 那就是他为什么来的原因。
    二、易错提醒
    注意不要一见到先行词为时间、地点、原因等，就用关系副词when, where, why 等，还要看它们在定语从句中充当什么成分。关系副词在定语从句中通常只能作状语，所以若定语从句缺主语或宾语，则不能选用关系副词，而要用关系代词，即使其前的先行词是时间、地点、原因等。如：
    Don’t forget the time (that, which) I’ve told you. 不要忘记我告诉你的时间。(that, which 用作定语从句 told的宾语，由于是作宾语，所以也可省略)
    He works in a factory that [which] makes TV sets. 他在一家电视机厂工作。(that, which 用作定语从句的主语)
    The reason that [which] he gave is different from yours. 他说的理由与你说的理由不同。(that, which 用作定语从句中gave 的宾语)
    注：在先行词 the reason 后除用关系副词 why外，也可用that(即使用作状语也是如此)。如：
    The reason why (that) they liked the restaurant was its anonymity. 他们喜欢那家餐馆的理由是它的默默无闻。
    That is the reason why (that) I asked you. 那是我询问你的理由。
    The reason why (that) she doesn’t like me is that I make her nervous. 她不喜欢我的原因是我让她紧张。
    The reason why (that) I’m asking is that I’m short of money. 我问的原因是我缺钱。

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