答案：D

题目分析：根据回答They’re fine, thank you.they是第三人称复数，所以问句中应该问they或者your mother and father也可以,故选CD，C. What are they 意思是他们是干什么工作的？与回答“他们很好，谢谢你”不符合，D. How are your mother and father意思是你父母怎么样？故选D。

点评 ：what are they? 相当于what do they do ?他们是干什么工作的，可以回答：My mother is a teacher and my father is a doctor.