当must用来表示对过去的情况进行“推测”(must + have done)时,如强调对过去情况的推测(一般句中有过去的时间状语),反意疑问句部分要用“didn’t + 主语”;如果强调动作的完成(一般没有过去时间状语),反意疑问句部分要用“haven’t / hasn’t + 主语”。
例:
You must have seen him at his birthday party yesterday, didn't you?(对过去情况的推测,且句中有过去的时间状语)
You must have seen him at his birthday party,haven't you?(强调动作的完成)