你问我答

摘要

1.问:—Do you still remember the day when we went to the Great Wall?—I can’t remember it well, but_{sometime last spring?A. might it be B. could it have been C. could it be D. must it have been老师,可以讲解以下这道题目吗?为什么一定要用have been呢?might或could本身不是已经是过去时了吗?}