英语选择题 谢谢 告诉一下原因啊

I don't know how to do it.
I don't know what to do about it.
所以选A

A what to do
意思是我不知道要怎么做
how to do 不加about

好像都可以, 意思都能说通
I don't know what to do about it -- 对此我不知道能做些什么
I don't know how to do about it -- 我对此束手无策

一楼正解