he was one of the greatest writers that had ever lived.此处为何用that而不用who引导

问题描述:

he was one of the greatest writers that had ever lived.
此处为何用that而不用who引导

我怎么觉得都可以呢。。。

先行词里有all,only,one of ,little,so,very...来修饰时,要用that.
这是我们上课做的笔记...