题目内容：

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

优质解答

你还能记起咱们去长城的那个日子吗?我记不清了,可能是去年秋天的时候吧?
could have done sth是对过去的推测,是情态动词的一种固定用法