要点1.如果主语是I,则反义疑问句用在宾语从句中.如：I think he is a doctor,isn't he?
要点2.如果主语不是I,则反义疑问句用在主句中.如：He doesn't think I am right,does he?
你的句子的答案是：I don't think he is a runner,is he?