关于as的用法,实在是搞不清楚,哪位帮我归纳下,

关于as的用法,实在是搞不清楚,哪位帮我归纳下,
例如;Some people have their lives greatly improved,as evidenced by the four children's graceful dressing,but their moral sense still remains unchanged or sometimes turns dramatically downgrading.这里的as是什么词性,

这里的as 是关系代词,引导非限制性定语从句,指代主句中的说过的或要说的意思,即“上述的这一点/正如上文所述”或“下文中提到的这一点/正如下文所述”.如：As is well known,the city is famous for its resplendent history.众所周知,这城市以它的光辉历史闻名于世.（这城市以它的光辉历史闻名于世,这一点是众所周知.）.
在这个句子中,as 指代上文说的Some people have their lives greatly improved
另附：关系代词as有如下两种用法：
一、与such,the same,as连用.如：
1.It wasn't such a good dinner___as_____she had promised us.
二、 引导非限制性定语从句,指代整个主句或主句的一部分.如：
2.__AS______is known to the world,Mark Twain is a great American writer.
3.The British are not familiar with different cultures and other ways of doing things,__as______is often the case in other countries.
as引导非限制性定语从句时,有以下特点：
1) as引导的从句可置于句首、句中或句末,如句2中的as从句置于句首,句3中的as从句置于句末.又如：
4.___AS_____might be expected,the response to the question was very mixed.
5.I hope all the precautions against air pollution,____as____suggested by the local government,will be seriously considered here.
6.A good many proposals were raised by the delegates,__as______was to be expected.
一些带有关系代词as的分句表达较为固定.例如：
as everybody knows
as you may remember
as you say
as I can see
as I have said
as I'm told
as you may have heard
再问： 谢谢，那as evidenced 中间是不是省略了个is啊，作为独立主格结构啊？
再答： as evidenced 中间是省略了个is ，但不是独立主格结构 --主语：as --谓语部分： evidenced by ...(其中省略了被动语态的助动词is) 2、因此可以改为—— It is evidenced by ... that .... This moment she felt her deep, as evidenced by the eyes, she knows that she is in love. 这一刻她深深的觉得她在，而那双眼睛就是证明，她知道，她是在爱着。