--___________Tomattheparty?--No.He___________bythetimeIarrived.A.Haveyo

--___________ Tom at the party?--No. He ___________ by the time I arrived.A.Have you seen; was to leaveB.Did you see; had leftC.Did you see; should have leftD.Have you seen; had left

B解析根据答语中by the time I arrived及第一个会话者说的地点状语可判断出，问句的谓语动词应用一般过去时态。答语中by the time表示“到某一时间”，其后的时间状语从句为一般过去时，主句动作发生在前，应用过去完成时。

就是这个解释