—You were brave enough to argue with Mr. Smith.
—Well, now I regret that.
A. to do
B. to be doing
C. to have done
D. having done
网友回答
A. to do
B. to be doing
C. to have done
(答案→)D. having done
解析：句意：--你和斯密斯先生争论真是很勇敢。--现在我后悔这么做了。Regret表示“后悔”的时候，后面接动名词做宾语，因为是已经做过了，用动名词的完成式，所以选D。