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
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D解析regret doing sth．后悔做过某事；regret to do sth．遗憾(抱歉)地要做……根据句意第一个空应该用动名词，这样排除了A、C项。动名词的否定形式是在动名词前面加not，故选择D项。