prep(1)像，如……一样(like;so as to appear to be)：dress/disguise sb～an officer把某人打扮/伪装成军官;die～a hero像英雄一样死去;talk～an old friend如老朋友一样谈话;rise～one man一个人一样站立起来;unite～one family团结如一家人;
(2)作为，当作，以……的身份(in the state，character，function，condition，job，etc of being)：work/serve/act～a lawyer当/当/充当律师;speak～a spokesman以发言人身份谈话;be famous/known～an eloquent orator作为雄辩的演说家而著名/闻名;a job/post～a manager 经理的工作/职位;treat/regard/accept/look on sb～a friend把某人当朋友对待/视为朋友/看作朋友/视为朋友;describe sth～a victory把……描绘成胜利;take/use sth～an example把……当作/用作例子;regard/think of sb～(being)happy认为/觉得某人幸福;look upon sth～very advanced把……视为非常先进;see sth～changing把……看作是不断变化的;
(3)作为，由于是(since sb is sth)：A～a doctor/a scientist/her son/his secretary，I should... 作为大夫/科学家/她的儿子/他的秘书，我应该……
(4)作为，当……的时候(when or while sb is sth)：A～a child/a school girl/a young woman，she showed every sign of genius.她年幼/是中学生/年轻的时候，充分显示出了天才的迹象。I used to eat a lot～a child but～an adult I eat little.我小时候吃得很多，可成人后吃得很少。
(5)以……的形式(in the form of)：A loaf goes into the oven～dough.面包放进烤炉时是面团。We all start life～babies.我们来到世上时都是婴儿。
adv(1)和(像)……一样(to the same degree or amount...as;equally...with)(用于adj或adv前，构成表示比较的as...as 结构)：1)(第二个as为连词)：run (twice/half/just/nearly)～fast as possible/as one can/as sb does/as one wants to 跑得尽可能/尽可能/和某人/与其愿望(的两倍/一半/正好/差不多)那么快;be(seem to be/look)(twice/...)～clever as one sounded on the phone/as one looks in the film/as before(似乎/显得)像电话里的声音所显得的/电影里的样子/从前(两倍/……)那样机灵;be～good an actress as one is a singer演技和唱歌水平一样好;be～eloquent a speaker as one's father is是一个和其父一样雄辩的演说家;need(get)(twice/...)～much money as one expected/as possible 需要(弄到)所希望/可能的(两倍/……)那么多的钱;catch (twice/...)～many(much) as one wants/as one can抓到想要/所能抓的(两倍/……)那么多;2)(第二个as为介词)：work(twice/...)～hard as they (or them)/as the other people干得有他们/别人(两倍/……)那么努力;walk(twice/...)～far as that走得有那(两倍/……)那么远;be(seem to be/look)(twice/...)～beautiful as that/as she(or her)/as one's sister(似乎/显得)如那样/她/其妹妹(两倍/……)那么漂亮;～brave as a lion/heavy as lead/loud as thunder/silent as the grave 雄狮般勇敢/铅一般重/如雷灌耳/死一般寂静;3)(第二个as引导的部分可省略)：Jack swims fast，but I swim just～fast.杰克游得很快，我也游得同样快。You have qualities that are just～important.你具有一些同样很重要的品质。She has a lot of money，but he has/hasn't～much.她有许多钱，他也有/没有那么多的钱。
(2)如同，像(not differently from;like)：A～before he remained unmoved. 一如既往，他一动不动。The “b” is silent～in “climb”.这个b如同在climb中一样不发音。
(3)例如(for example;such as;like)：Some flowers，～the rose，require special care.有些花，例如玫瑰，需要倍加精心。
conj (1)当……的时候(at the time that;while)：A～he walked/was walking along he met an old friend.他正走着的时候，突然遇见了一个朋友。I watched her～she combed her hair.她梳头时，我注视着她。She closed her eyes～she uttered the words.她说这话时闭上了眼睛。
(2)因为，由于，既然(because;since;for the reason that)(通常位于句首，语义不如because 和since强)：A～he was obviously ill，we called the doctor.由于他显然是病了，我们就叫了大夫。A～you are tired，you had better rest.既然你累了，就最好休息一下。He couldn't come～he had another appointment.他来不了啦，因为他另有约会。
(3)虽然，尽管(although;regardless of the degree to which)(置于句首的形容词或副词之后)：Rich～(或though) he is，he is not happy.尽管他有钱，但并不幸福。Much～(或though) I want to，I cannot go.虽然我很想去，却去不了。Try～you will，you won't manage it.无论你怎么努力，你也对付不了。
(4)按(依)照;像，如(in the same way or manner in which)：Do～I say/I told you to/you are told/I do.照我说的/我告诉你的/告诉你的/我这样做。He doesn't speak/think/work～other people do.他说话/考虑问题/工作和别人不一样。Leave the room～it is.让房间保持原来的样子。
(5)(引导关系从句)1)(用于same...as句式中)：I got the same grade～(或that)you (got).我得了和你一样的分数。We drove out by the same road～we had entered by.我们的车从来时走的那条路开了出去。My stand on this is just the same～it was before/four years ago.我在这件事情上的立场和以前/四年前的一样。2)(用于such...as句式中)：Such women～knew Tom thought he was charming.认识汤姆的女人都认为他有魅力。He is not such a fool～he looks.他并不像看上去那么傻。I never heard such stories～he tells.我从未听过他讲的那种故事。3)也是，同样(and so too)(通常后接be或do+主语)：David is tall，～are my brothers.大卫个子高，我的几个兄弟也个子高。Mary is old，～is her husband.玛丽老了，她丈夫也老了。Jack is a teacher，～was his wife before she had children.杰克是教师，他妻子有孩子以前也是教师。
(6)按照……(in accordance with what)：Norway，～described in this advertisement，seems to be a wonderful place for a holiday.根据这则广告所描述，挪威似乎是个度假的好地方。Cyprus，～we all know，is an island in the Mediterranean.塞浦路斯，众所周知，是地中海的一个岛屿。He is a teacher，～is clear from his manner.从他的举止可以清楚看出，他是教师。
(7)犹如，如同(what;in the way that)(表示比例或关系)：2 is to 8～4 is to 16.2比8就如同4比16。A～some are rich，(so) others are poor. 既有富人，就有穷人。
as against 而 …… 则……(表示对比)：The money earned this week amounts to ￡100～against ￡80 last week.本周赚了100英镑，而上周则是80英镑。
as for 至于：A～for going back，that is quite out of the question.至于回去，那是根本不可能的。
as from，(esp AmE) as of 自(某日)起：A～from/of today you are in charge.从今天起你负责。
as it is 事实上：I would have liked to have finished by May，but～it is， that is impossible.我本想5月前完成的，实际上那是不可能了。
as it were 可以说：He is，～it were，a walking dictionary.他可以说是一本活字典。
as to/regards 至于：A～to(doing)that，I haven't decided yet.至于做那件事，我还没有决定。He said nothing～regards whether he would come back.至于是否回来，他什么也没说。
as yet 至今尚未：The danger was～yet not serious.危险还不严重。
as if /though 似乎，好像：You look～if/though you had seen a ghost.你的样子就好像见了鬼一样。He talks～if/though he knew everything.他说话的神气就好像他什么都知道似的。He raised his hand～if to command silence.他举起一只手好像要命令大家安静下来。
【用法】adv(1)的用法(as...as)多为肯定式;也可以为否定式，不过，有人坚持认为此时副词(第一个)as应改为so为好，如(注意not的位置)：He won't leave as/so soon as she will/as she (or her).(他不会像她那么快离开的。)It's not nearly as/so cold as it was yesterday/that.(今天不大像昨天/那样那么冷。)
【辨异】 1)as与like2 都可用作介词，但此时as的本义为 in the role of(以……的身份)，如：die as a hero(死得是个英雄——就是英雄);like则意为“像”，如：die like a hero(死得像个英雄——指表现像英雄);as还可用作连词(后接从句或介词短语);而like 则不可(其后仅可接名词短语)，如：die as a hero does(像英雄那样(英勇)就义)，又如：Do it like me/Do it as I (do).(像我一样做。)但是，在非正式英语中，like也可用作连词，代替as(以及as if)(不过这种用法一般认为应避免)，如：It happened as/like you said it would.(事情正如你所说的那样发生了。)He acted as if /like he was afraid to go home.(他那样子就好像他害怕回家似的。)2)as，because与since和for都表示原因。because表示直接的原因，语气最强，可用来回答 why 的问题(其他几个皆不可)，如：I was sleeping because I was tired. as和since则表示附带的原因，经常置于句首，如：As/Since I was tired，I was sleeping.for较as和since正式，表示一个事后想起的原因，对前一句所陈述的事实进行补充说明，与前一句为并列关系，如：I was sleeping，for I was tired.