as可以引导定语从句,但是它引导的定语从句有固定的搭配:
1)先行词由the same,such修饰时,定语从句可以用as来引导;例如:
She wore the same dress as her young sister wore.
He is such a good boy that everybody likes him.
2)as引导定语从句时的固定搭配
as we (all) know/ as is known to all
as far as sb.is concerned,
例如:As we all know,China is a developing country.
3) as引导非限制性定语从句可置主句首,主句尾或主句中,而which引导非限制性定语从句只能置于句尾或句中,不能置于句首.
同时,as也可以引导让步状语从句.表示尽管之意.在这种情况下,as引导的从句可以倒装,倒装时形容词可以提前.例如:
As he is young,he can't carry the heavy box.
=Young as he is,he can't carry the heavy box.