— When you the smart hat?— While my parents were waiting for the plane at the airport.A. d

问题补充：

— When you the smart hat?

— While my parents were waiting for the plane at the airport.

A. did, buy B.do,buy C.were,buying

答案：

解析：句意:根据下文,当我的父亲正在机场等飞机的时候.可知上文描述的是过去某时发生的动作,故用一般过去时态,选A.