一、引导词as, which的区别
1．引导非限制性定语从句，指代整个主句内容时的区别：
(1)表达“正如”之意时，用as，如果仅指代整个主句内容而没有“正如”之意，则用which。
He went abroad, which was unexpected.
他出国了，这让大家感到很意外。
She is a good doctor, as her mother used to be.
她是一个很出色的医生，和她母亲当年一样。
(2)当从句位于主句前面时，只用as。
As is known to everybody, the moon travels round the earth once every month.
2．限制性定语从句中有such, the same时，其后常用as引导定语从句(the same后也可用that，但意义不一样)。
He is such a good teacher as we all love and respect.
他是一个我们都爱戴和尊敬的好老师。
