这句话是什么从句?

题目

这句话是什么从句?
"Those who are playing an important part is well known to us all."
顺便帮我分析一下这句话,哪儿是主句哪儿是从句,

答案

"Those( who are playing an important part )is well known to us all."
括号内是定语从句,其他是主句.