【题目】He had known the matter before you told him, so you _________ have told it to him.
A.mustn'tB.can'tC.needn'tD.shouldn't
在线课程【答案】C
【解析】
考查情态动词。句意：在你告诉他之前他已经知道了这件事，因此你本不必要告诉他的。A. mustn't不必；B. can't不能；C. needn't不需要；D. shouldn't不应该。根据句意可知， 表示不必要而做了做的事，needn't have done 表“本来不必要做某事却做了（对过去的虚拟）”，故选C。