问题补充：
I regret hard at school, or I would have succeeded in passing the exam.
A. not to work
B. having not worked
C. to have not worked
D. not having worked
答案：
A. not to work
B. having not worked
C. to have not worked
(答案→)D. not having worked
解析：regret doing sth.后悔做过某事；regret to do sth.遗憾（抱歉）地要做…
