◎ 题干
— 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
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“— 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…”主要考查了你对  【一般现在时】【过去进行时】【过去完成进行时】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。