must have done ：對過去事實的推測,不是現(xiàn)在完成（后者不能與明確的過去時間連用）.反義問句是問“昨天他們是否做了家庭作業(yè)”,當然用didn't they.
比較：
They have done their homework,haven't they?
They did their homework yesteday,didn't they?
They must have done their homework yesterday,___?
They must have done their homework yesterday,___?
為什么是didn't they?
我覺得應(yīng)該是haven't they啊?
為什么是didn't they?
我覺得應(yīng)該是haven't they啊?
英語人氣：954 ℃時間：2019-10-20 00:09:23
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