It must have rained yesterday
昨天一定下过雨了.
must 情态动词
1.必须. you must study hard.
2.禁止. You mustn't walk on the grass.
3.可能性. 表示推测.“一定”
1) must do/be. 对现在的动作或状态推测.
He must be Tom.他一定是Tom.
2) must be doing.对现在的正在进行的动作推测.
Tom must be sleeping now. Tom 现在一定在睡觉.
3) must have done.对过去的动作或状态推测.
Tom must have stayed up yesterday.Tom 昨天一定熬夜了.
否定形式 can not /could not