请教either or的问题

Either Perry’s faction or Tucker’s faction, but not both, will win control of the government, lf Perry’s faction wins, the nation wins, the nation will suffer economically. lf Tucker’s faction wins, the nation will suffer militarily.

    Given the statements in the passage, which one of the following statements must be true?

(C)If is certain that the nation will suffer either economically or militarily, and also certain that it will not suffer both..

(D)If the nation suffers militarily, it is possible, but not certain, that Tucker’s faction has won control of the government.

正确答案是D.怎么排除C啊?

还有 either A or B和 either A or B, but not both 有什么区别? 好搞啊...

(C)If is certain that the nation will suffer either economically or militarily, and also certain that it will not suffer both..

这句话有问题，题目没说nation只有这两个选择啊，也许有第三方的选择。题目只讲了，有这两种选择，这两种选择对应的是什么。

所以D里面有it is possible, but not certain

对哦, 没想仔细.

谁知道either A or B和 either A or B, but not both 的区别吗? 新东方上课时没听明白