Can't, Must, and Cant, With Have and the Past Participle of the Verb

Must or can't plus an infinitive both help us to express a strong belief that something is or isn't possible. When we're less sure about something, we can say, for example, the fossils might not, mightn't, or may not be from a known human species. For each of these sentences, choose might, must or can't to fill the gap. I hope you got them all right.