关于一道疑问代词的英语选择题there are so many kinds of computers in the sh

关于一道疑问代词的英语选择题
there are so many kinds of computers in the shop. I really don't know ( )to choose.
A what B which C how D where
此题答案选B
我们知道which 表示哪一个,但如果选C似乎也说的过去,可以翻译为“我真的不知道该怎样选择?”
在我映像中如果选择C,后面必须加it,变成how to choose it?
为什么加it,请详细说明.