关系代词as与which的用法区别 (1) 引导限制性定语从句时，在such, as, the same后只能用as，其他情况用 which：I never heard such stories as he tells. 我从未听过他讲那样的故事。It’s the same story as I heard yesterday. 这故事跟我昨天听到的一样。
This is the photo which shows my house. 这张照片拍的是我的住宅。

(2) 引导非限制性定语从句时，有时两者可互换：
I live a long way from work, as [which] you know. 我住得离工作单位很远，这你是知道的。

(3) 但在，在以下情况引导非限制性定语从句时，两者不可换用：① 当从句位于主句前面时，只能用 as：As is known to everybody, the moon travels round the earth once every month. 月球每月绕地球转一周，这是每个人都清楚的。② as 引导的非限制性定语从句应与主句在意义上和谐一致，which无此限制：He went abroad, as [which] was expected. 他出国了，这是大家预料到的。他出国了，这是大家预料到的。He went abroad, which was unexpected. 他出国了，这让大家感到很意外。(不用as)③ as 引导非限制性定语从句时，先行词通常不能是主句中某个具体的词，而应是整个句子、整个短语或某个短语推断出来的概念，而which 则无此限制：The river, which flows through London, is called the Thames. 这条流经伦敦的河叫泰晤士河。(不用as)④ 当as 引导非限制性定语从句作主语时，其谓语通常应是连系动词，而不宜是其他动词，而 which
She has married again, as [which] seemed natural. 她又结婚了，这似乎很自然。

She has married again, which delighted us. 她又结婚了，这使我们很高兴。(不用as)