问题补充：
I have always regretted harder at school.
A. not to study
B. to not study
C. having not studied
D. not having studied
答案：
A. not to study
B. to not study
C. having not studied
(答案→)D. not having studied
解析：考察动词regret用法。动词regret后面要接两个结构，regret to do sth遗憾要做某事；regret doing sth=regret having done sth遗憾做了某事；句意：我总是后悔在学校里没有认真学校。动名词的否定式就是在动名词前面直接加not。故D正确。
