问题补充:
--Have you ever been here before?
---Well, I once here for four years. Those days are really unforgettable.
A. have stayed
B. had stayed
C. have been staying
D. stayed
答案:
A. have stayed
B. had stayed
C. have been staying
(答案→)D. stayed
解析:考查时态。根据语境及时间状语for four years可知,用一般过去时。句意:——你以前来过这里么?——嗯,我在这里呆过四年,那些岁月真的难忘。