I really don't know ___about it.A.what to do ;B.how to do 为什么正确答案是A呢?请大家帮我详细分析下.宾语从句不是what to do和how to do

I really don't know ___about it.A.what to do ;B.how to do 为什么正确答案是A呢?
请大家帮我详细分析下.
宾语从句不是what to do和how to do

因为what是代词,在这儿相当于do的宾语,由于已经有宾语了所以about it 加在这儿相当于宾语补足语或者修饰成份（不知具体算哪种）
how是副词,在这儿相当于to do it how（不妨用另外一个副词,如：secretly,代替）,how 作为副词修饰动词do.