定语从句中which 做不做成分?

这里你所说的定语从句中的which是关系词,具体地说,是关系代词.关系词在定语从句中有三个作用：
1,引导定语从句；
2,代替先行词；
3,在定语从句中担当一个成分.
关系代词which在定语从句中做成分,既可以做从句的主语又可以做从句的宾语:
1. Football is a game which is liked by most boys.（which做从句的主语）
2. This is the pen (which) he bought yesterday.（which做从句的宾语,可省略）