【题目】When walking down the street, I came across David, whom I _____ for years.
A.didn't see
B.haven't seen
C.hadn't seen
D.wouldn't see

【答案】C
【解析】句意：当沿着街道散步的时候，我遇见了多年未见的David。根据语境，“not see”这个动作发生在come across之前，是过去的过去发生的动作，用过去完成时。故选C。