二、引导限制定语从句时which与as的区别：
1.先行词如为表示物的名词或代词，在从句中又做介词的宾语时，只能用which。例如：
This is the pan in which I boiled the milk.这就是我煮牛奶的锅。
2.前面有as时，引导定语从句的关系代词用as,不用which。例如：
There are as many dictionaries as are needed.所需要的字典都有了。
3.前面有such时，引导定语从句的关系代词用as，不用which。
1）Such women as know Tom thought he was charming.认识汤姆的女人都认为他很迷人。
2）I have never heard such stories as he tells.他讲的那些故事我从没有听过。
3）He is not such a man as I expected.他不是我期望的那种人。
1. 前面有the same时，引导定语从句的关系代词用as而不用which。例如：
1）We are facing the same problems as we did years ago.我们现面临着和多年以前同样的困难。
2）This is the same wallet as I lost.这只钱夹子与我丢失的那只相同。
3）I have the same trouble as you have.我和你有着同样的困难。
总之，which与as引导定语从句的区别要在实践中多体会，体会多了，才能正确运用。