as与which引导非限制定语从句
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一、as引导非限制性定语从句
as引导非限制性定语从句，代替整个主句，对其进行说明，但通常用于像as we all know，as it is known，as is know to all，as it is，as is said above，as always mentioned above，as is usual，as is often the ca，as is reported in the newspaper等句式中。as在非限制性定语从句中作主语、表语或宾语，且引出的从句位置比较灵活，可位于句首或句末，也可置于主句中间。通常均由逗号将其与主句隔开。as有“正如……，就像……”之意。如：
The gentleman put on a hat when leaving his hou, as was usual in tho days.
在那些天里，那位绅士就像往常一样在离开家时带上一顶帽子。（as在从句中作主语）
He forgot to bring his pen with him, as was often the ca.
他忘了带笔，这是常事。(as在从句中作主语)
He is absorbed in work, as he often was.
他正在全神贯注地工作，他过去经常这样。(as在从句中作表语)
As we all know, the earth is round. 众所周知，地球是圆的。(as在从句中作宾语)
The two brothers were satisfied with this decision, as was agreed beforehand.
两兄弟都对此项决定满意，这项决定事先已达成一致。(as在从句中作主语)
注意：as引导限制性定语从句与非限制性定语从句的区别：
1．as引导限制性定语从句常用于下列句型中，在从句中担当主语、宾语或表语。
(1)so/as/such+tried名词+as...“像……一样的，像……之类”；
(2)the same+名词+as“和……音乐会英文一样的”
I want to buy the same motorcycle as you have. 健康的英文我想买和你一样的摩托车。
This book is not such as I expect. 这本书不是我所期望的。
Such things as you described are rare now. 如你所描述的这样的事情现在是罕见的。
Our factory needs such uful machines as we saw in the exhibition. 我们在展会上看到我们工厂需要的这种有用的机器。
2．as引导非限制性定语从句，指代的是整个主句，经常用在一些习惯表达中。
This is my basic idea, as was mentioned before. 这是我的基本观点，就像先前提到的。
二、which引导的非限制性定语从句
关系代词which在非限制性定语从句中所指代和修饰的可以是主句中的名词、形容词、短语、其他从句或整个主句，在从句中作主语、动词宾语、介词宾语或表语。
1．which指代主句中的名词，被指代的名词包括表示物、婴儿或动物的名词、表示单数意义的集体名词以及表示职业、品格等的名词。如：
The apple trees，which I planted three years ago，have not borne any fruit.
这些苹果树是我三年前栽的，还没有结过果实。(which指代主句中的名词The apple trees)唯一的英文
She is an artist，which I am not. 她是一位艺术家，而我不是。
（世界语词典which指代主句中的名词artist）
That book, which is the novel I was reading last week, is the one I meant for you to take to the beach with you.
那本书，就是我上周看的小说，是我想让你带到海边的那本。
（which指代主句中的名词That book）
2．which指代主句中的形容词。如：
She was very patient towards the children，which her husband ldom was.
她对孩子们很耐心，她丈夫却很少这样。（which指代主句中的形容词reader是什么意思中文patient）
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She is always careless，which we should not be.
她总是马虎大意，我们可不应该这样。（which指代主句中的形容词careless）
3．which指代主句中的某个从句。如：
He said that he had never en her before，which was not true.
他说以前从没见过她，这不是真的。（which指代主句中的宾语从句he had never en her before）
4．which指代整个主句。如：
In the prence of so many people he was little ten, which was understandable.
在那么多人面前他有点紧张，这是可以理解的。（which指代前面的整个主句）
He may have acute appendicitis，in which ca he will have to be operated on.
他可能得了急性盲肠炎，如果是这样，他就得动手术。（which指代前面的整个主句）
三、as与which引导非限制性定语从句的异同
1．相同点
两者引导非限制性定语从句时，可指代主句中的部分或整个句子的内容，在从句中作主语、宾语或表语，位于主句之后有时可互换。
(1)The meeting was put off, as/which was exactly what we wanted. 会议被推迟了，这正是我们想要的。
(2)He was a doctor, as/which I knew from his manner. 他是一个医生，这是我从他的举止上看出来的。
(3)As can be en from his skin, he must be from Africa.
=He must be from Africa, which/as can be en from his skin.
从他的皮肤可以看出，他一定是来自非洲。
2．不同点
(1)as可以放在主句前后，也可插入主句之中；而which引导的非限制性从句只能位于主句之后。如：
As is planned, we got there before eight. 正如计划，我们在八点钟之前到达了那儿。
After graduating from college，I took some time off to go travelling，which turned out to be a wi decision. 大学毕业后我抽出一部分时间去旅游，事实证明这是一个明智的决定。
(2)当which引导的从句在意义上近乎并列关系时，可以用and this，and that代替，意思是“这件事”。如：
He changed his mind, which(and this, and that) made me very angry. 他改变了主意，这使我很生气。
She has married again, which(=and this, and that)academician was unexpected. 出乎意料的是，她又结婚了。
而as主要起与上下文连接的作用，表达说话人的看法、观点，并指出主句内容的出处或根据等，例如：
Einstein, as we know, is a famous scientist. 爱因斯坦，众所周知，是位伟大的科学家。
As is announced in today’s newspaper, we must improve our style of work. 今天的报纸上说，我们必须改进工作作风。
(3)which在非限制性定语从句中作主语时，可用各类动词作谓语；而as作主语时，谓语常用系动词，如be，em，become等，一般不用其他行为动词。例如：
He married her, which was natural.（可用as代替which）
他和她结婚，这是很自然的事。
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He won a/the Nobel Prize in chemistry, which made him illustrious.（不可用as 代替which）
他获得了诺贝尔化学奖，这使他名扬天下。
He didn’t say anything at the meeting , as/which emed very strange. 他在会议上什么也没说，这看起来很奇怪。
(4)在非限制性从句中，which后的be动词不可省；而as后的be动词可以省略。
She told me she won the match, which was a lie. 她告诉我她赢得了比赛，这是个谎言。
The material is elastic, as (was) shown in the figure. 这种材料是有弹性的，就像图中所示的。
(5)在as引导的从句中，后面的动词常常使用被动语态，如果从句行为动词是主动语态，一般用which引导定语从句)。如：
He has been late again, as is expected.
Allen has made great progress, which delighted us. 艾伦已经取得了很大的进步，这让我们很高兴。
(6)在非限制性定语从句中which可以指代主句中某一个单词，as不可以。
My brother enjoyed playing basketball, which he really plays well.
我哥哥喜欢打篮球，他真的打得很好。(which代指主句中的basketball)技能培训
