第2个回答 2011-08-11
as引导定语从句,其实不是专指限定性定语从句。而是一种特殊的定语从句。
as做关系代词,主要分3种:
1:构成such...as的结构。可以看做是固定表达,所以不能用that替换as。
e.g. We have such apples as you never saw.我们有你从未见过的苹果.
2:such 和as连在一起,也可以看做是固定表达,不能替换that。
e.g. There was a look of fear in his eys,such as people have when they are suddenly awakened.
他眼中透露出一种人们突然被叫醒时,露出的惊恐。
3:as可以单独引导定语从句,指代整个句子。
e.g.He was a foreigner, as I knew from his accent.
从他的口音中,可以听出是个外国人。as指代He was a foreigner的整个句子。
关于that:
在限定性定语从句中,作为从句的先行词,是不能用逗号和主句隔开的。
另外,that指代的名词,在主句中通常做主语或者宾语。这时可以和which替换。
e.g. These are the books which/that I ordered.
如果有介词提前,也就是从句的介词放到先行词的前面,只能用which不能用that。