There are so many kinds of mp5 in the shop

A
重新整理了一下
这题主要不是考意思的区别了
如果要选B的话,应该改成 which one to buy
例如：I can't decide which one to buy ,because there are so many toys for me to choose. 我不能决定到底买哪一个玩具,因为这里有太多的玩具让我挑选.cant应该是can't 才对.
表示在多个中择一
因为后文的回答是We can not decide（）,分析句子结构已经具有完整的主语与谓语,那么后文不可能再出现一个谓语,因此只能用不定式或者动词ing形式充当宾语
句子可以变成We can not decide to buy ()=we can not decide () to buy
因为句中缺少一个宾语,所以后文必须还它一个宾语,这里可以用
what相当于something that,指代上文的MP5
或者是用which one,one作为实际宾语,which作为形式宾语