问题补充：
He Shanghai, for I saw him talking with the headmaster a moment ago.
A. must have gone to
B. can’t have gone to
C. mustn’t have been to
D. can’t have been to
答案：
A. must have gone to
B. can’t have gone to
C. mustn’t have been to
(答案→)D. can’t have been to
解析：can’t have done表示对过去的行为动作的否定，从上文来看“根据我所了解的情况，他们不可能这个假期很快乐”，A项表示“可能已经，该已”，B项表示“过去该做而未做”，C项表示“本来不需做而实际上做了”。
