三、as 引导的定语从句
as可以作关系代词用,引导一个定语从句。as 在从句中作主语、宾语或表语。as引导的定语从句常常出现在same， such等词之后。例:
We want such materials can bear high temperature and pressure.
A） that B） as C） what D） which
（1999年全国大学生英语竞赛初赛题） B对。我们需要能耐高温高压的材料。
You must show my wife the same respect as you show me.你必须尊重我的妻子,就象尊重我一样。(as在从句中作show的宾语)
We drove out of the town by the same road as we had entered by. 我们沿着进城时的路开车出城。(as在从句中作by 的宾语)
Such women as knew Tom thought he was charming. 认识汤姆的女人都说他翩翩动人。(as在从句中作主语)
Do you think children should read such books as are recommended to them by their elders你认为儿童必须读长辈向他们推荐的书吗?(as在从句中作主语)
The boy became a math wizard such as had never been heard of before. 这孩子成了前所未闻的数学奇才。(such和as连在一起)
There were so many tickets available as were asked for. 有足够的票,可满足需要。
as可以没有具体的一个先行词,而是指一种情况;这时as代表主句中的一部分或整个主句。例:
Feeding， clothing， educating and providing jobs for the young is therefore a major problem， as is restricting the rate of population growth in the future. 吃饭、穿衣、年青人的教育和就业是个大问题,而将来限制人口增长率也是个大问题。(as指 a major problem; as 从句中,as 作表语, restricting 短语作主语。)
I attempted for about fifteen minutes ， as was usual with me ， to take notes but at the end of that time I threw my pen and paper away and lived only in the inspiration of the hour.头十五分钟里我像往常一样,试图做记录,但最后我抛开了笔和纸,整个身心沉浸在当时的激动之中。
He came from Guangzhou， as I knew from his accent.他是广州人,这点我从他的口音可以知道。
He is a professor， as is clear from his manner. 从他的举止来看,很清楚:他是个教授。
He opposed the plan， as had been expected. 他反对这个计划,这是意料中的事。
as 指一种情况时,as从句还可以置于句首或句子中间:
As we have seen ， oceans cover more than 70 percent of the earth.我们已经知道:海洋占了地球面积百分之七十以上。
As has been mentioned above ， an object has positive charge when it has lost electrons.如上所述:物体失去电子时带正电荷。
The size of the audience ，as we had expected， was well over one thousand. 听众大大超过一千人,这是意料之中的。
which 和 as都可引导非限制性定语从句;which 和 as 在非限制定语从句中,可以没有一个具体的先行词,而指一种情况,但它们的用法不同:
We grow all our own fruit and vegetables， save money， of course.
A） which B） as C） that D） what
（B6，1991.6-60，A对。） 我们自己用的水果和蔬菜全部自己种,这当然省钱。（which 指We grow all our own fruit and vegetables）
as 指一种情况时,有“如,正如”的含义,常常以as is known ， as might be expected， as can be seen 类似的形式出现,as 指一种情况,这时其位置灵活,可置于主句的前部、中部或后部:
As is known to all， light travels much faster than sound. 正如人人皆知的那样:光的传播要比声音快得多。
He aGREed with you， as could be expected. 正如可以预料到的那样,他同意你的意见。
Fish is what I want ， as are bear's paws.鱼,我所欲也;熊掌,亦我所欲也。（as 的意思是what I want。）
主句含否定意义,as指一种情况且as从句处于句子中间或后部时,as从句并不含否定意义。例:
The unit of a language is not ，as was once commonly supposed ， the word， but the sentence.语言的单位不是词,是句子;而过去曾经普遍认为语言的单位是词。
She did not ，as her friend had feared， open the case.她的朋友很害怕她(当面)打开盒子,而她并没有(当面)打开。
Spiders are not insects， as many people think， nor even nearly related to them.许多人以为蜘蛛是昆虫,而实际上它们不是昆虫,甚至与昆虫几乎没有关系。
试比较下面句子中,as从句与主句的否定意义是一致的:
As can be seen from the samples given ， there is no simple answer to any of these questions. 从所给的例子来看,所有这些问题都没有简单的答案。
As has been said above， grammar is not a set of dead rules. 正如前面所说,语法不是一套死条文。
(本节内容曾发表在《英语学习》1992年第9期)
