“情态动词+have done”怎么用

1.must have done表示对过去已经发生的事情进行肯定的推断,只用于肯定句中,意为"一定,必定",其否定形式为cannot have done。It must have rained last night,for the road was quite wet.昨晚肯定下雨了,因为路面十分潮湿。I saw Mr.Wang just now.He couldn’t have gone abroad.刚刚我还看见王先生了,他不可能已经出国了。