先行词是指事物的不定代词， 如：all, everything, something, anything, nothing, none, one, much, little等， 或先行词中受到这些词以及the only, the very, the same, the last 等词修饰限制的指事物的名词理， 关系代词只能用that.We know nothing that happened here yesterday.先行词指物并受到序数词或形容词最高级修饰或是形容词转化的名词时， 关系代词只用that不用which.This is the best thing that has been used against pollution.当先行词既有人又有物只用that.Do you know the things and persons that they are talking about?
定语从句关系词有什么作用
