Module 6 Unexplained Mysteries of the Natural WorldGrammar情态动词+have done的用法归纳 【探究寻规】选词填空,并观察其规律。 couldn’t, needn’t, should, might, must1. Come on!You ______ have finished this task hours ago. 2. She suddenly fell down on her way to school;she _____ have been ill. 3. She ________ have seen me because I wasn’t there at all yesterday. shouldmust..