在定语从句里,as既可以引导非限定性定语从句,也可以引导限定性定语从句.as在两个里面都是作关系代词.
(1)非限定性定语从句:用法同which,用来指代前面的句子(而非先行词),多与know/expect/see搭配使用.
e.g.As we know,smoking does harm to our health.
(2)as引导限定性定语从句,多与the same/such/so搭配使用.
e.g.I have got into the same trouble as he has.
另:which和as的区别
A.which不能放句首(The sun heats the earth,which is very important to us.)
B.as如果在从句中作主语,后面的谓语动词必须是系动词.(It rained hard yesterday,which prevented me from going to the park.这边就不能用as来代替which,因为prevent是行为动词)