题目如下：
Among the butane conformers , which occur at energy minima on
a graph of potential energy versus dihedral angle ?
(A) gauche only (B) eclipsed and totally eclipsed
(C) gauche and anti (D) eclipsed only
(E) anti only
答案是C
题意应该是问丁烷的构形中，哪一种二面角会产生最稳定的能量
不是应该是anti才对吗
为什么答案不是E 而是 C 呢?