what引导的从句是宾语从句
what在从句中充当主语
what=the + 名词 + that （名词根据句意而变,本句意为the person that)
who引导名词从句是“谁”的意思.
如果要先B,
改为
the person who is known as ...就对了.
She is the person who is known as a nosy person...
又如：
This place is what is called Mount Tai.（这地方就是被叫做泰山的地方.what=the place that)