—— Do you still remember the day when we went to the Great Wall?
—— I can’t remember it well, but＿＿＿＿＿＿sometime last autumn?
A. might it be
B. could it have been
C. could it be
D. must it have been
网友回答
A. might it be
(答案→)B. could it have been
C. could it be
D. must it have been
解析：could have done表示对过去发生情况的可能性推测。