out和happen的区别？

break out，爆发;越狱;逃跑;摆脱

例句

The authorities have urged people to stock up on fuel in case hostilities break out.

当局已敦促人们储存燃料，以防战事爆发

happen，v.作为结果)发生;碰巧;恰好;

例句，

All these changes happened over a period of time.

所有这些变化都是在一段时间内发生的。