— Do you still remember when we went to Nanjing?
— I can't remember now but sometime last summer?
A. might it be
B. could it be
C. could it have been
D. should it have been
网友回答
A. might it be
B. could it be
(答案→)C. could it have been
D. should it have been
解析：情态动词加现在完成式，表示对过去的推测，could表可能性，should表过去该做而没做的事。