as的这种用法常见于以下这些结构:as we can see,as can be seen,as we know,as is(well) known,as may be imagined,as often happens,as has been said before,as was mentioned above,as is often the case,as/indeed it is
1.引导限制性定语从句和非限制性定语从句
(1)as多与such或the same连用,可以代替先行词是人或物的名词。
(2)as 也可单独使用,引导非限制性定语从句,作用相当于which。例如:
The elephant’s nose is like a snake,as anybody can see.
(3)the same…that与the same…as在意思上是不同的。
2.As引导的非限制性定语从句的位置
as引导的非限制性定语从句位置较灵活,可以位于主句前面.中间或后面,一般用逗号与主句隔开,但which所引导的非限制性定语从句只能放在主句之后。例如:
(1) As is expected,the England team won the football match.
(2) The earth runs around the sun,as is known by everyone.