1. as在限制性定语从句中的应用
As 用作关系代词或关系副词引导限制定语从句时，主要用在 “such (+ n.) + as …”（和…同样的），“the same (+ n.) + as …”（像…这样的，像…这/那的），“the same as”（同样的人、事），“such as”（这样的东西或人）等结构中，as在从句中可以作主语、宾语、表语和状语。
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结构
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例 句
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the same (+ n.) + as …
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We do the same work as they (do). 我们和他们干同样的活。
We go the same way as they do. 我们和他们走的是同一条路。
He is reading the same book as I did yesterday. 他正在读的书和我昨天读的书一样。
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the same …that…
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He is reading the same book that I read yesterday.
他正在读我昨天读的那本书。
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such (+ n.) + as …
such as…
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Such people as knew Mary admired her. 认识玛丽的人都钦佩她。
He is not such a fool as he looks. 他并不像他看起来那样傻。
I haven’t much money but you can use such as I have.
我并没多少钱，但你可以用我手头的这些。
Such of us as knew him will regret his death.
我们所有了解他的人都会哀悼他的去世。
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as…as
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He smokes as expensive a cigarette as he can afford.
他抽一种他买得起的最贵的香烟。
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2. as与which引导的非限制性定语从句中的区别
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as从句
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which从句
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1. as只指代整个主句。
2. 引导从句时表示“正如”，没有具体的内容。
3. 从句的位置很灵活。
Air, as is well-known, is a gas.
众所周知，空气是气体。
The night has turned cold, as is usual around here.
夜晚变得冷，在这一带通常如此。
Water is boiling at 100ºC, as is shown in the figure. 如图所示，水在100ºC时沸腾。
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1. which 既可指代整个主句又可指代主句中的一部分。
2. 引导从句时表示具体的内容。
3. 从句只能放在主句之后。
He changed his mind at the last moment, which made me angry.
他在最后一刻改变了主意，这是我很生气。
I called him by the wrong name, for which mistake I apologize.
我叫错了他的名字，对此我表示道歉。
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3. as引导的非限制性定语从句常常成为一些惯用句型：
as was discussed before 如前所述
as is reported / announced in today’s papers 据今天的报纸报道
as is / has been pointed out 正如所指出的那样
as is shown in the figure 如图所示
as has / had been said before 如前所说
as may be imagined 正如可以设想的那样
as is well-known 众所周知
as we all can see 正如我们有目共睹
