请英语高人解答Which的用法

问题描述:

请英语高人解答Which的用法
The anti-government group,which monitors human rights violations on both sides of the conflict via a network of contacts across Syria,

which引导定语从句.后面的长句都是用来描述前面的the ...group 的.为什么不用whowho 只用于修饰人。