should another world war break out ,what would become of human beings?

问题描述:

should another world war break out ,what would become of human beings?
前面的should 和后面的would
也就是这个句子的虚拟语气的用法
关于前面的倒装问题,我不太懂

当形容一些事情很少很少机会发生,会用should,在此句同 "if" 一样,假作 "如果",