must be和must have be有什么区别

题目

must be和must have be有什么区别
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答案

简单地说：对过去情况作推测,用must have been；所对现在情况作推测,用must be.比较：He must be ill. 他一定是病了.（指现在有病）He must have been ill. 他当时一定是有病 / 他一定生过病.（指过去有病）He must ...