--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
网友回答
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。