关系代词as用法

关系代词as用法
 
一、引导限制性定语从句
用在 such, same, as 等之后,引导限制性定语从句。如:
I live in the same place as Tom does. 我和汤姆住在同处。
He’s not such a fool as he looks. 他并不像看上去的那样愚蠢。
He smokes as expensive a cigarette as he can afford. 他抽一种他买得起的最贵的烟。
二、引导非限制性定语从句
(2) 单独用作关系代词,引导非限制性定语从句,可放在主句之前、之后或中间,且主从句之间一般要用逗号隔开。如:
As was expected, he succeeded at last. 正如我们所料,他终于成功了。
I had coffee after dinner, as is my usual practice. 我饭后喝咖啡,这是我的习惯。
Freddie, as might be expected, was attending the conference. 弗雷迪在参加会议,这是可以预料到的。
三、aswhich的用法区别
引导限制性定语从句的区别:as用作关系代词引导限制性定语从句时,它通常只用于 such, same, as 等之后,而which 用作关系代词引导限制性定语从句时,则用于除 such, same, as 之外的其他结构。
引导非限制性定语从句的区别:which引导非限制性定语从句时,通常只能位于主句后,而as引导的非限制性定语从句位于主句之前、之后或中间。
根据从句谓语动词的特点来看,as在定语从句中作主语时,从句谓语通常要有be或别的系动词,但which不受此限制。如:
Li Ming was late, which (=and this) made Mr. Zhang very angry. 李明迟到了,这件事使张先生非常生气。(不可用as)
根据句意的逻辑性来看,as引导的定语从句只表示一个众所周知或意料之中的事,但which不受此限制。如:
He married her, as [which] was natural. 他和她结婚了,这是很自然的。
He married her, which was unexpected. 他和她结婚了,这是出乎意料的。(不可用as
本文摘自《中学英语高频词详解词典》

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