as...as的用法
as...as意为"和……一样"，表示同级的比较。使用时要注意第一个as为副词，第二个as为连词。其基本结构为：as+ adj./ adv. +as。例如：
(1)This film is as interesting as that one.这部电影和那部电影一样有趣。
(2)Your pen writes as smoothly as mine.你的钢笔书写起来和我的一样流畅。
其否定式为not as/so +adj./ adv. +as。例如：
This dictionary is not as/so useful as you think.这本字典不如你想象的那样有用。
若有修饰成分，如twice, three times, half, a quarter等，则须置于第一个as之前。例如：
Your bag is twice as expensive as mine.你的袋子比我的贵一倍。
几个关于as...as的常见句型：
(1)as...as possible Please answer my question as soon as possible.请尽快回答我的问题。
(2)as...as usual/before She looks as pretty as before.她看起来和以前一样漂亮。
(3)as long as... (引导条件状语从句)
It took us as long as three years to carry out the plan.我们花了长达三年的时间才完成这项计划。
(4)as far as
He walked as far as the railway station yesterday evening.昨天傍晚，他一直散步到火车站。
(5)as well as She cooks as well as her mother does.她烧菜烧得跟她母亲一样好。
一些带有as...as结构的常见短语归纳：
as busy as a bee像蜜蜂一样忙碌 as easy as ABC像ABC一样容易 as deep as a well像井一样深
as light as a feather像羽毛一样轻 as soft as butter像黄油一样软 as rich as a Jew像犹太人一样富裕
一、“as(否定句中可用so)＋adj．／adv．＋as…”，其基本意思为“……和……一样”。但在实际应用中，此结构在不同的语境中含义差异较大。
1、表示不同人或物同一性质的比较，意为“……和……一样……"。
The tree is as tall as the building(is)． 这棵树和那栋楼一样高。
Michael is as bright as George(is)． 迈克尔和乔治一样聪明。
2、表示同一个人或物不同性质的比较，意为“既……又……”
Alice works as happily as(she)plays(happily)． 艾丽丝愉快地工作，尽情地玩。
Danny is not so wise as he is witty． 丹尼为人风趣，但欠明智。
3、用于表示两个人或物不同性质的比较，表示程度相同或相当，意为“……而……”。
He was as handsome as his wife was beautiful． 他长得非常英俊，他的妻子也长得非常漂亮。
He was as experienced as his brother was green． 他经验丰富，而他兄弟却涉世未深。
二、as…as结构的另一种形式是“as much／many＋名词＋as＋从句”。
Mary has written as many essays as her brother． 玛丽写的文章篇数和她弟弟一样多。
It is as much your fault as your wife’s． 这既是你的过错，也是你妻子的过错。
Henry is as much a hypocrite as·John． 亨利跟约翰一样是个伪君子。
三、若有修饰成分，如twice，three times，half，a quaer等，必须置于第一个as之前。
You are not half as clever as you think you are．你可不像自己想象的那么聪明。
She isn’t going out with a man who is twice as old as she．
她不打算和一个比她大一倍的人出去散步。
You’ve made just as many mistakes as I have． 我和你犯的错误一样多。
We’ve produced twice as much cotton this year as we did lastyear. 我们今年的棉花产量是去年的两倍。
四、as…as结构的另一变体形式是“as＋形容词原级＋名词词组＋as”
I don't want as expensive a car as this.＝I don't want a car as expensive as this． 我不要这么贵的汽车。
Tony is as clever a boy as his brother． 托尼是一个和他兄弟一样聪明的男孩。
五、当as…as与表示重量、数量、时间、距离、价格等的计量名词连用时。往往并不表示比较。而是构成一个形容词组，意为“重达……，多达……，高达……”等。
The river is as deep aslO meters． 这条河深达10米。
Frosts often occur as late as May． 往往到5月份还有霜。
六、“as+原级+as any(或ever)”、“as+原级+as…can be”、“nothing(或no)＋so＋原级＋as…”等结构表达的是最高级意义。即在某种程度上或某方面达到极限或最大限度。
He is as great a mathematician as any． 他是一位非常杰出的数学家。
He is as happy as happy can be． 他幸福无比。
No one is so deaf as those who won’t listen． 最聋者莫过于不听劝说的人。
七、as…as…不表示比较的几个常见句型。
1．as…as possible／sb can尽可能的……
Please answer my question as soon as possible．
请尽快回答我的问题。
The detective is searching the man as carefully as he can．
那个侦探正在尽可能仔细地搜查那个男子的身体。
2．as…as usual／before像以前一样……
She looks as pretty as before．
她看起来和以前一样漂亮
Though they failed，they still worked as hard as usual．
尽管他们失败了，但他们仍像以前一样努力工作。
3．as long as只要，引导条件状语从句
Ｉ will stay with you as long as there is a room flree．
要是你有一间空余的房子，我就住在你这里。
You may borrow this book as long as you promise to give itback．
只要你答应归还，你就可以把这书借走。
2. as用作连词引导时间状语从句
as与when，while都是引导时间状语从句的从属连词，含义都是"当……的时候"。但它们有区别：用when时，从句的动作可以与主句的动作同时发生，也可以先于主句的动作发生；用while时，从句的动作为一过程，主句动作与从句动作同时进行或在从句动作过程中发生；用as时，主句和从句的动作同时发生，具有延续的含义。例如：
(1)It was snowing when he arrived at the construction site.他到达工地时，天正在下雪。
(2)He was watching TV while his mother was cooking.他母亲做饭时他在看电视。
(3) You will grow wiser as you grow older.你会随着年龄的增长而越来越聪明。
3. as用作连词引导原因状语从句
as，because，since都可以表示因果关系，连接原因状语从句，含义是"因为，由于"，但它们有区别：because表示的语气最强；as一般放在句首，语气较弱，较口语化；since常常用在书面语中，表示多为对方已知的、或稍加分析便可得知的原因，有时可译作"既然"。例如：
(1) He will succeed because he is in earnest.他一定会成功，因为他很认真。
(2) Since you are so sure of it he”ll believe you.既然你对此如此有把握，他会相信你的。
(3) As rain has fallen, the air is cooler.因为下过雨，空气比较清爽。
4. as作连词引导让步状语从句
as与although (或though)，however (或no matter how)等都可以引导让步状语从句，含义是"虽然，尽管"，但它们有区别：although语气稍正式些，可放在句首，也可放在句中，主句中不能再用but，但可以用yet；as所表示的语气较强，引导的让步状语从句用倒装语序；however引导让步状语从句时，它的后面可跟形容词或副词，也要用倒装语序。例如：
(1) Although he is quite old, he still jogs every day.他虽然年纪相当大，仍然每天慢跑。
(2) Strange as it may seem, nobody was injured in the accident.这次意外虽然显得令人不可思议，却没有人受伤。
(3) However hard he may try, he will not attain his goal.无论他怎样努力也达不到目标。
二、as作关系代词的用法
关系代词as引导定语从句时，既可以单独使用，也可以与其他词连用，其用法要比that和which更为复杂。
1. as引导定语从句与其他词连用
①用于the same...as结构中
This is the same book as I read last week.这本书和我上周读的那本是一样的。
②用于such...as结构中
I don”t like such books as he recommends.我不喜欢他推荐的那些书。
③用于"so +adj. + a/an + n. (单数) + as "结构中
I am not so strong a man as I was.我已经没有从前那么强壮了。
2. as单独引导定语从句
as单独引导定语从句时，先行词可以是一个词，也可以是一个句子或短语。例如：
(1) She is late, as is often the case.她迟到了，这是经常的事。(先行词是整个主句)
(2) To shut your eyes to facts, as many of you do, is foolish.对事实视而不见--你们好多人都是如此的愚蠢。(先行词是不定式短语)
三、as作介词的用法
as作介词，意思是"作为"，"以……身份"。例如：
He came to China as a tourist five years ago.他五年前以游客的身份来过中国。
四、as作副词的用法
to the same degree or amount; equally "相同地"，"同样地"。例如：
They don”t have as many airplanes.他们没有同样多的飞机。
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