I would have attended your birthday party last night but for the fact that it at that time．
A. was raining
B. would rain
C. had rained
D. had been raining
网友回答
(答案→)A. was raining
B. would rain
C. had rained
D. had been raining
解析：句意：要不是昨晚这个时候一直下雨，我可能已经去参加你的生日聚会了。I would have attended your birthday party last night表过去本可以做某事，实际上没做，是虚拟语气，而the fact后面是同位语从句，说明事实的内容，不能用虚拟语气，所以用一般过去式，选A。