THAT NIGHT refers to a particular night in the past. I think MUST HAVE BEEN is the grammatical one, since it refers to the past, but MUST BE is not unheard of and is possible in casual English/informal English, though not possible in formal English. Do you agree?
Thank you.
Top answer
Yes , must have been. I'd be quite surprised to hear a native speaker say 'must be'.
— Clive
Yes , must have been.
I'd be quite surprised to hear a native speaker say 'must be'.
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