must have done 是对过去发生的动作最有把握的猜测,意思是“一定”,例如：走到门外看到地上湿的,便猜“刚才一定下过雨了”,英语就是 It must have rained.把握差一点的用should； 例如地上不是太湿,你猜“刚才应该下过雨吧.” It should have rained.把握再差一点的用may:It may have rained.“刚才可能下过雨”.最不肯定的用might:It might have rained.