一、as用作關(guān)系代詞引導(dǎo)定語從句
1. as 引導(dǎo)非限制性定語從句，一般不指代某個具體的名詞或代詞，而是代表整個主句或主句的一部分。這種從句可放在主句之前，也可以放在主句之后，有時還可以放在主句的中間。如：As is reported in the newspapers, talks between the two countries are making progress. 正如在報紙上所報道的，兩國間的談判有所進(jìn)展。Grammar is not a set of dead rules, as has been said above. 如上所說，語法不是一套死條文。Spiders are not insects, as many people think, nor even nearly related to them.蜘蛛不是昆蟲，盡管許多人都這樣認(rèn)為，它甚至與昆蟲幾乎沒有聯(lián)系。2. as 引導(dǎo)限制性定語從句，主要用于the same…as（與……相同），such…as（像……一樣），as…as（與……一樣）。如：（與She knew he felt just the same as she did. 她知道他的感受和她一樣。Such a man with a good temper as Mr. Li is is easy to get along with. 像李先生這樣好脾氣的人是容易相處的。He smokes as expensive a cigarette as he can afford. 他抽一種他買得起的最貴的煙。
二、as作為從屬連詞引導(dǎo)時間狀語從句
表示“當(dāng)……的時候”或“>一邊……一邊”，強(qiáng)調(diào)主句的動作和從句的動作同時發(fā)生。如：I saw him as he was getting off the bus. 當(dāng)他下公共汽車的時候我看見了他。The boy was singing a popular song as he was bicycling. 這男孩邊騎車邊唱歌。As she grew older, she became less active. 當(dāng)她長大一點的時候，就變得不那么活潑了。As she grew older, she became less active.
三、as作為從屬連詞引導(dǎo)原因狀語從句
as 引導(dǎo)的原因狀語從句常放在主句前，表示“因為，由于”。如：As she is a model teacher, she gives a good example to others. 因為她是一名模范教師，她給其他人樹立了一個好的典范。As he wasn’t ready in time, we went to the cinema without him. 由于他沒有及時準(zhǔn)備好，我們就去看電影了，沒有等他。
三、as作為從屬連詞，引導(dǎo)讓步狀語從句
as引導(dǎo)讓步狀語從句比較特別，它要求將主語和謂語或謂語的一部分倒裝。如：Old as he is, he is still full of energy. 盡管年紀(jì)大了，但他依然精力充沛。Try as she may, she never succeeds. 盡管她很努力，但總是不成功。Try as she may, she never succeeds. Much as I admire Mr. Wang as a poet, I don’t like him as a man. 盡管我喜歡王先生的詩歌，但我不喜歡他的為人。注：當(dāng)?shù)寡b后置于句首的名詞為單數(shù)可數(shù)名詞時，習(xí)慣上不帶冠詞。如：Boy as he was, he was made king. 盡管他還是個孩子，卻被立為國王了。
四、與其他詞搭配使用構(gòu)成從屬連詞引導(dǎo)從句
1. as if / as though。表示 “好像，仿佛”，引導(dǎo)表語從句或方式狀語從句。如：It looks as if / as though it is going to snow. 看起來要下雪啦。He looks as if / as though he had seen a ghost. 他的臉色看起來好像他看見了鬼。He talks as if /as though he knew everything about it. 他說話的口氣好像他已經(jīng)全部都知道了。< it. about everything>
2. as [so] long as。“只要”，引導(dǎo)條件狀語從句。如：< it. about everything>As [So] long as you can keep away from them, you will be safe. 只要你能遠(yuǎn)離他們，你就安全了。I’m happy as long as you are happy. 只要你幸福，我就感到幸福了。I’m happy as long as you are happy.
3. as [so] far as。表示“在……的范圍內(nèi)”，引導(dǎo)限制狀語從句。多用于下列結(jié)構(gòu)：as [so] far as I know（據(jù)我所知），as [so] far as I can see, as [so] far as I’m concerned（依我看）。如：（依我看）。如：As [So] far as I know, the couple have been abroad for about five years. 據(jù)我所知，這對夫婦已經(jīng)約五年了。There’s only one thing to be done now, as far as I can see. 依我看。現(xiàn)在只有一件事情要做。
4. as soon as。表示“一……就”，引導(dǎo)時間狀語從句。如：As soon as he got off the plane, he telephoned her girl friend. 他一下飛機(jī)就給他的女朋友打了個電話。He started as soon as he received the news. 他一得到消息就出發(fā)了。
總之，由于as的用法復(fù)雜，同學(xué)們在學(xué)習(xí)時一定要注意比較其在不同句子中的作用，判斷其連接的是什么樣的從句，多做一些關(guān)于相關(guān)練習(xí)，這樣便可掌握其用法了。
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