问题
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
B:could it have been
C:could it be
D:must it have been
正确答案是：
