Question

He must have finished it yesterday, didn't he?

为什么不是 haven't he?
或者hasn't he?

为什么原句不讲： He must finish it yesterday

Answer 1

must have done 是对过去发生的动作最有把握的猜测，意思是“一定”

在must have done 句型中 其反义疑问句 有两种情况
对已发生的过去情况的推测，若陈述句谓语部分有“must have done”，而且有表示过去的时间状语，问句部分用didn't；若没有表示过去的时间状语，问句部分用haven't或hasn't。如：
1)They must have gone there last night,didn't they?
2)They must have arrived by now,haven't they?（根据by now来判断）
3)They must have been to the Great Wall,haven't they?

Answer 2

情态动词+完成时表示对过去的判断。
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