aren't you?
当主句部分谓语动词为think,believe,guess,疑问句应和从句的人称时态保持一致（主句时态必需是一般现在时）；但如果主句的时态是过去时等等,疑问句应和主句的人称时态保持一致.
I think chickens can swim,can’t they?
I think Lucy is a good girl,isn’t she?
I didn't think he was happy,was he?
I thought he was a teacher,didn't