That problem is the most difficult ---- all

问题描述:

That problem is the most difficult ---- all
用of 还是among
答案上是among
是不是答案错了
那为什么不能用OF呢

就是among
三者或三者以上都用among
among all 突出了唯一
例句:Among all kinds o fruit,I like apple best.
所有的水果当中我最喜欢苹果.