I need something for cutting the paper.Oh,you want a knife?O

I need something for cutting the paper.Oh,you want a knife?Ok,l'll get ______ for you.
I need something for cutting the paper.
Oh,you want a knife?Ok,l'll get ______ for you.
A.it
B.that
C.this
D.one
it 强调前面提到过的东西,前面不是出现过刀了吗（you want a knife）

是不是one啊答案~
one是一个,不是特指,knife不一定非得找到特定的那个,只要随便找到一个刀子就OK了吧.
it给人的感觉就是你必须找到那个特定的、你上文提到的刀子,别的刀子不可以.
以上是我的理解.