as作关系代词
不仅可以代替一个名词，而且可以代替整个句子或一件事，通常译作“正如这一点”，“如……一样”。
As is known to everybody, the moon travels around the earth once every month.
如同大家所知道的一样，月亮每月围绕地球旋转一次。
As has been said before, grammar is not a set of dead rules.
如同以前说过的一样，语法并不是一套死规则。
Such a clever girl as she can learn anything quickly.
像她这样聪明的女孩子学任何东西都很快。
It was absolutely bad manners to get into people's room without knocking, as quite a few young people are doing every day.
不敲门就进入别人的房间绝对是不文明的行为，现在很多年轻人每天都这么干。
as构成固定词组
1. as可以构成介词词组
as against 与……相比；as compared with 与……对比；as for/to 至于，关于；as from/of 自……起；as a resultof 由于……的结果；as regards 至于
As regards salary, I leave it to you to decide after experience of my capacity.
关于薪水，请你们考验本人能力后再作定夺。
The output amounts to ten thousand dollars as against eight thousand last year.
和去年八千美元的产量相比，今年的产量达到了一万美元。
There is no doubt as to who will be elected.
至于谁会当选，这是毫无疑问的事。
The only exception was the year of 1991, when there was a slight decline as compared with the previous year.
唯一例外的是1991这一年，与前一年相比略微有所降低。
As a result of your carelessness, the whole project should be put off at least one month.
由于你的粗心，整个计划将要被推迟至少一个月。
2. as可以构成副词词组：
as above 如上；as follows 如下；as a matter of fact 事实上；as a whole 就整体来说；as good as 和……几乎一样，实际等于；such / so … as to 这样的……以至于……；as yet 尚，至今还（用于否定句）；as well 也
As a matter of fact, he didn't have any interest in the project.
事实上，他对这个项目一点兴趣都没有。
I am not so foolish as to make such a promise.
我还没有愚蠢到会许下这样的承诺的地步。
His mother was so ill that she was as good as dead.
他的母亲病得很厉害，就跟死了一样。
3. as构成词组作关系代词：
as...go 就……一般情况来说；as it is / was 事实上，按现状；as it were 仿佛是
He is quite good, as boys go.
就一般男孩子而言，他已经很好了。
I thought conditions would get better, but as it was, they were getting worse.
我以为情况会好转，但事实上，却是越来越糟糕。
He was, as it were, intoxicated by the soft air and sunshine of spring.
他仿佛像往常一样陶醉于春天温馨和煦的阳光和空气里。
4. as可以构成连词词组：
according as 根据，按照……而；in as (so) far as 根据……程度
You may go or stay, according as you decide.
你可以自己决定是去还是留。
In as (so) far as we have known about the matter, we can make a decision after the meeting.
就我们对这件事情的了解程度，我们可以在会后作出一个决定。