问题
选择题
They must have been here the day before yesterday,＿＿＿＿?
A．mustn’t they
B．didn’t they
C．mustn’t have they
D．had they
答案
答案：B
must have done表示对过去发生情况的肯定推测，句中带有明确的过去时间状语，故附加疑问句用“didn’t they”。
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