在非限制性定语从句中,as 可放于句首或句中,而Which只能放句中.
He got the first prize,which surprised us.( 此句中which指的是He got the first prize这个句子）
He lived in a small house,which faced south.(此句中which指的是house这个单词）
在非限制性定语从句中,as只指句子意思,如：
As we expected,he won the first prize.或 He won the first prize,as we expected.