a,英语语言习惯是这样吧,不要用中国思维去想（这样想的人估计会选b和c）
我自己是到了一定程度时候可以靠预感选的,没有多少材料给你对比,找了其他资料给你看看,因为我以前都是觉得英语很麻烦,哈哈,要懂得总结哦
下面是复制别人的,希望你以后遇到类似的问题可以自己解决
带as(so)… as的结构
1.在表示“和…一样…”时,可用“as...as”结构(前面的as后要用原形)：
He is as busy as before.他还是和以前一样忙.
I’ll give you as much help as I can.我将尽量帮助你.
The airport was as crowded as ever.机场还是像平常那样拥挤.
You’re as good a singer as Johny Buck.你的歌唱得像约尼∙伯克一样好.
Modern computers can be as small as a book.现在的电脑可以像一本书那样大.
2.在表示“不像…那样…”时可用“not as(so)...as”这种结构：
It isn’t so cold as yesterday.今天不像昨天那样冷.
He is not so handsome as his brother.他不像他哥哥那样英俊.
I’m not so experienced as you think.我没有你想的那样有经验.
The situation is not so bad as had been painted.形势没有描绘的那样糟糕.
Jack is not as(so) old as he looks.杰克不像他看起来那样老.
3.这种结构中也可包含一个状语或有almost,just,nearly,quite这类副词形容：
The whale was twice as long as her boat.那头鲸有她的那艘船的两倍长.
Their house is about three times as big as ours.他们的房子约为我们房子三倍大.
My command of English is not half so good as yours.我的英语掌握得还不及你的一半好.
He was almost as diligent as his sister.他几乎和她姐姐一样勤奋.
She is nearly as tall as her mother.她几乎和她妈妈一样高.
4.as...as还可用在许多固定说法中：
as brave as a lion
as busy as a bee
as vain as a peacock
soft as velvet
as bright as day
as fat as a pig
as gentle as a lamb
easy as ABC
另外找了别的固定搭配 关于 so as 跟so that 的,其实很简单的
Tom is _so_ good a student _as_ is often praised by the teacher.
Jack is _so_ smart a boy _that_ he can work out difficult maths problems quickly.
so……as中as必须在从句中担任成分（主语、宾语等）,而从句就是我们熟悉的定语从句咯.
so……that中的that 不能在从句中担任成分,只是单纯的先行词,从句也就不算定语从句了.
