—You were brave enough to argue with Mr. Smith—Well now I regret that.A. to doB. to b

问题补充：

—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

答案：

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。