请问：AS等引导的定语从句、状语从句是怎么省略的?

定语从句一般不省略.
状语从句的省略分两种情况：
1.主句主语和从句主语一样,从句动词有Be动词.
When he was watching the movie,he heard a loud sound.
----When watching TV,he heard a loud sound.
2.从句主语是it,有Be动词.
If it is necessary,I will buy this product.
---If necessary,I wll buy this product.
As引导的定语从句并不省略,我举个例子：
As you know,he is a pretty loyal soldier.
As 引导定语从句并且在从句中做动词know的宾语.

你说的是不是这种情况：See the answers as given at the end of this book.
这里面“as given”作定语修饰answers，可以看做是“as are given”的省略形式。
提个意见，以后再求助的时候给些例句，有时候只靠语言来表达不是很清楚。