问题补充：
for the fact that she broke her leg, she might have passed the exam.
A. Hadn it been
B. Had it not been
C. Was it not
D. Were it not
答案：
A. Hadn it been
(答案→)B. Had it not been
C. Was it not
D. Were it not
解析：选B句意：要不是她摔断了腿，她可能就通过考试了。根据题干中的broke, might have passed可推知设空处为与过去事实相反的虚拟语气。与过去事实相反，if从句谓语动词应为“had＋过去分词”，故排除C、D两项；如果虚拟语气的if从句为否定句，省略if时，只需将助动词、were或情态动词提前构成倒装，而否定词not需保持在主语之后，故排除A项。
