as在引导非限制性定语从句时的用法几乎和which差不多,但有两点需注意, 1)as可位于句首,which不行 2)as往往表顺其自然的事情,也就是肯定句或表示肯定意思的句子,如:As we had expected,he married her. He married her,which we hadn't expected. as在引导限制性定语从句时也主要是两种用法 1)such+先行词+as的从句 2)the same+先行词+as的从句 关于第二条,需要注意若是同类用as,若是同一用that如 He bought the same pen as I had. He found the same pen that he lost.