问题补充：
sat down for a rest the door bell rang.
A. Hardly I had; when
B. Hardly I had; than
C. Hardly had I; than
D. Hardly had I， when
答案：
A. Hardly I had; when
B. Hardly I had; than
C. Hardly had I; than
(答案→)D. Hardly had I， when
解析：Hardly…when…表示“一……就……”，位于句首时，主句要倒装。
