赖世雄教你学英语语法
关系词
6-7: as可代替主句
单独使用as时，as亦可做关系代词，等于which，用以代替整个主句。
例：he is nice, which is known to us.
= he is nice, as is known to us.
（他人很好，我们都知道。）
he works hard, which we all know.
= he works hard, as we all know.
（他很用功，我们都知道的。）
但使用as取代which时，要注意下列要点：
1. as 引导的从句可置于主句的前后，而which引导的从句则只能置于从句之后
例：he is nice, which we all know.
= he is nice, as we all know.
= as we all know, he is nice.
which we all know, he is very nice.(x)
2. as+be+p.p.时，be动词可以省略
例：he is nice, which was mentioned before.
= he is nice, as was mentioned before.
= he is nice, as mentioned before.
（从前说过了，他人很好。）
3. 注意下列特殊例子
例：he was drunk (as usual./as is usual with him.)
（和以往一样他又醉了。）
his conditions are (as follows./as what follows.)
（他的条件如下。）
第二例中，不管前面的名词是单数或复数，动词是现在时、将来时或过去时，as follows中的动词follows一定要用单数现在时。
例：he listed the names (as follows./as what follows.)
（他列出的名单如下。）