My coat and my umbrella please.Here is my ticket.Thank you, sir.Number five.Here's your umbrella and your coat.This is n...

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Lesson 3 Sorry,sir. My coat and my umbrella please. Here is my ticket. Thank you ,sir.Number five. Here's your umbrella ...

must have been:是对过去的推测这里最重要的是最清楚must 和 have been 之间的关系。must 后面本来就是要跟动词原形，而have been本来就是完成时的原形。must/should/could/would ha...

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