2011英语四级语法讲义大全：定语从句二

三、在定语从句的非限制性定语中，which 和as 是容易混淆的。在很多情况下两者兼可互换，但在下列情况中不可互换：

1、通常As 可以放在整句的句首，而which，只能在逗号之后，as 本身含有“正如”，as 在定语从句中既可是主语也可做宾语

As appear from her paper ,she has read widely in Romantic literature.

She is remarkable, as I have told you .

2、 which 在做非限制性定语从句关联词时可以无明确先行词，指前句整个的意思，如：she has warried again,which surprises us .

四、在定语从句中，许多人往往分不清all that 和what,what 实际上只引导名词性从句，它相当于all that两个字，例如：

All that I know is that he has made up his mind to heave the country for a new place.

 = what I  know is that ……

、限定性定语从句：