反义疑问句的的选择题20.I am very interested in Mark Twain's novels,---

反义疑问句的的选择题
20.I am very interested in Mark Twain's novels,_____?这道题我选B
A.aren't I B.am not I C.aren't you D.are you
但是它的正确答案是A的.为什么,我区分不开A跟B的答案,因为我记得我们老师说过这么一个例子：I am the right man for the job.am I not?
那为什么20题要选A