英语语法总结：as用法总结
在阅读中，你是否会经常碰到as，并不知道如何理解？当我们记一个单词时，主要是了解单词的音、形、义和词性。as的音形很简单，意思和词性就是我们需要重点研究的。as共有三种词性：介词、副词和连词。as的词性不一样，意思也是不一样的。下面华慧考博老师就来结合例句一一理解。
华慧考博英语语法总结：as用法总结
一、as可以是介词，意思是“作为，当作”介词后面只能加名词或者动名词。那么如何在句子中判断as是介词呢？很简单，只要看到as后面接的是名词或名词短语，那就是介词的用法。
as作为介词的用法
used to describe the fact that sb/sth has a particular job or function 作为；当作
•I respect him as a doctor. 我尊敬他这个医生。
•Drugs will be the saving of a few—as a last resort.毒品将是少数人的救星—作为最后的手段。
•As the defining epidemic of a modern age notable for overconsumption and excess, obesity is hard to beat.
作为一个以过度消费和过度饮食著称的现代流行疾病，肥胖是很难战胜的。
二、as作为副词，主要是用于as…as…结构中，其中第一个as就是副词的用法。修饰形容词或副词、
华慧考博英语语法总结：as用法总结
as... as...used when you are comparing two people or things, or two situations （比较时用）像…一样，如同
Eg：He was as white as a sheet. 他面无血色。
•She doesn't play as well as her sister. 她演奏得不如她姐姐。
•As always, he said little. 他和平时一样，少言寡语。
三、as作为状语从句的连词，可以引导状语从句和定语从句。如果as引导状语从句，句式结构是这样的：_________as___________.或者as________, __________.这个横线表示一个完整的句子，as必须连接两个完整的句子。
3.1.时间状语从句
while sth. else is happening 当…时；随着，表示主从句的动作同时发生。
•He sat watching her as she got ready. 他一直坐着看她准备停当。
•As she grew older she gained in confidence. 随着年龄的增长，她的信心增强了。
3.2.方式状语从句
in the way in which 照…方式；按照
•They did as I had asked. 他们是按照我的要求做的。
•Leave the papers as they are. 别去动那些文件。
•She lost it, just as I said she would. 我就说了吧，她把它丢了。
W: Yes, sometimes we use an antibiotic, but you aren't sick enough to make that worthwhile.
华慧考博英语语法总结：as用法总结
有时我们会使用抗生素，但你病得还不够严重，不值得使用抗生素。
M: What? I am sick as I want to be.
什么？（你说我生病不够严重，难道）我能按我想的方式生病吗？
3.3.原因状语从句
used to state the reason for sth.因为；由于；表示双方都是知道的原因。
•As you were out, I left a message. 你不在，所以我留了一张字条儿。
•She may need some help as she's new. 她是新来的，可能需要一些帮助。
3.4.让步状语从句
used to say that in spite of sth. being true, what follows is also true 尽管；虽然；即使.as
引导状语从句，需要倒装。Though可倒可不倒，although不能倒装。
•Happy as they were, there was something missing. 尽管他们很快乐，但总缺少点什么。
•Child as he is, he knows a lot=Though/Although he is a child, he knows a lot.
尽管他是个孩子，但是他懂得很多。
•Getting people to change their behavior takes time and effort, held back as we are by our biological tendency to eat more than we need, and by the food industry's ruthless opportunism in exploiting that.
尽管吃得比我们需要的多的生物倾向，以及食品工业无情的机会主义在利用这一点，阻碍了我们，但是让人们改变行为需要时间和努力。
华慧考博英语语法总结：as用法总结
3.5.比较状语从句
•Tesofensine works by inducing a sense of fullness, is twice as effective as any other drug at enabling patients to lose weight.
特索芬（一种减肥药）的作用是使人产生饱腹感，在使患者减肥方面的效果是其他药物的两倍。
四、as可以连词，也可以引导定语从句
4.1. as引导限制性定语从句，需要和the sane…as…;such…as…; as…as…搭配使用。
•She started giving the same answers as were given by the others.她开始给出和其他人给的一样的答案。
•We have found such ingredient as is used by them.我们已经找到了像他们采用的那种原料。
4.2. as引导非限制定语从句，as可以指代一个句子，as从句可以放在主句前面，后面，或者插在主句中间。翻译成为“正如，就像”
•As required in new Orleans, the patient in emergency should be sent to a nearby hospital.
正如新奥尔良的要求的，紧急病人应该被送到附近的医院。
•As demonstrated in our special issue on economic growth, technological fixes will not compensate for excessive consumption.
正如我们关于经济增长的特刊所证实的那样，技术改进（原文中指代减肥药的研发）不会补偿过度消费。
英语语法总结：as用法总结
•But the cancer cells contained no DNA whatsoever from the father, __53__ would be expected if she had inherited the cancer from conception.
53.A. whatB. whomC. whoD. as
答案选D，as指代前面的一句话，as从句放在了指代这句话后面。句意是：但是癌细胞中没有任何来自父亲的DNA，如果她从怀孕中遗传了癌症，这是可以预料的。