Let's get the key ___the question? ----OK.Let's start.

问题描述:

Let's get the key ___the question? ----OK.Let's start.
A:for B;withC:on D:to
书上说正确答案是D,请问为什么要选D呢?

固定用法,表示什么什么的钥匙、的关键、的答案、的控制权……等等,a/the key__某物时,都是to