as在引導(dǎo)非限制性定語從句時的用法幾乎和which差不多,但有兩點需注意,
1）as可位于句首,which不行
2）as往往表順其自然的事情,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在引導(dǎo)限制性定語從句時也主要是兩種用法
1）such+先行詞+as的從句
2）the same+先行詞+as的從句
關(guān)于第二條,需要注意若是同類用as,若是同一用that如
He bought the same pen as I had.
He found the same pen that he lost.