Question

— 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

Answer 1

　　　C　

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。