as的用法详解
A. adv. to the same degree or amount; equally 同样地，一样地
He was angry, but she was just as angry.
=She was as angry as he was.
他生气了，但她同样生气。
He has a lot of time but I don’t have as much (as he does).
=I have less time than he has.
他有很多时间，但我没有那么多。
B. prep.
(1) in the same way as; like像，如同
Everyone rose as one.
=everyone rose together.
大家一起同时起立。
I only like such small animals as cats and dogs. 我只喜欢像猫和狗一类的小动物。
as和like在汉语中都译做“像”，但字面下的隐含意思是不同的。
like侧重A与B两者间的比较，并不意味着A和B属于一类或完全相似。
He speaks English like an Englishman.
=He speaks English in a way an Englishman speaks English.
他说起英语来有些像英国人。
as则侧重于同一性，意味着A与B两者属于同一类或完全相似。
He speaks English as an Englishman.
=He speaks English as well as an English.
他说起英语来和英国人一样好。
She was dressed as a man. 她打扮成了男人。(俨然她就是个男人了)。(相同事物)
She was dressed like a man. 她像男人那样穿衣服(依然可见她是个女人)。(不同事物)
(2) in the capacity/job/role/character/condition/function of以...身份，以...为职业，扮演...角色，具有...特性，在...状态下，起...功能/作用
As a schoolboy, he showed every sign of genius. 当他还是个小学生的时候，就显示出了天资聪慧。
The forest will act as a defense against desert dust. 森林能起防御沙漠灰沙的作用。
The news came as no surprise. 这消息来得并不突然。
The man was described as tall and dark, and aged about 20. 据描述这男人高个子，深色皮肤，年龄在20岁左右。
They regarded the lecture as boring. 他们认为讲座很乏味。
Many people use education as a steppingstone to a better life.许多人将教育作为赢得更好的生活的手段。
I used to look on him as a friend. 我以前把他看作是一位朋友。
C. conj.
(1) to the amount or degree that 像...一样(引导比较状语从句)
The fabric was as soft as silk. 那件织品软得像丝绸。
(2) in the way in which 以...方式，如同...那样(引导表语从句和方式状语从句)
It is as you told me. 事情正如你告诉我的那样。
Do in
(3) in spite of the fact that, though虽然，尽管(引导让步状语从句)
(a) adj./v-ed2/v-ing+as+主语+系动词。如：
Oldest as he is in the office, he works hardest.尽管他是办公室里年龄最大的，他工作最努力。
注意：adj./adv.最高级前应省去定冠词the。
Well-written as the book is, the author is not satisfied and prepared to revise it.尽管这本书写得很好，作者还是不满意并打算修改它。
(b) adv.+as+主语+谓语部分。如：
Much as I admire his courage, I don’t think he acted wisely.我虽然崇拜他的勇气，但我认为他这样做是不明智的。
(c) n./pron.+as+主语+系动词。如：
Student as he is, he does not study hard.他虽然是个学生，却不努力学习。
You can use my bike, such as it is. 尽管我的自行车不好，请将就用吧。
注意：单形可数n.[c, s]前应省去冠词a(n)。
(d) 动词原形+as+主语+谓语的其它部分(时态助动词/情态动词)。如：
Try as you will, you won’t be able to persuade him.不管你怎么努力，你都说服不了他。
(4) at or during the time that; when; while当...的时候；随着...(引导时间状语从句)
He slipped as he was walking to his car. 当他走向车子时，他摔倒了。
He became stout as he grew older. 随着年龄的增长，他发胖了。
(5) for the reason that; because, since因为(引导原因状语从句)
She may need some help as she's new. 他可能需要帮助，因为他是新手。