◎ 题干
He ______ when the UFO arrived. He didn't wake until the UFO disappeared.

[     ]

A. slept
B. was sleeping
C. was doing homework
D. was singing
◎ 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“He ______ when the UFO arrived. He didn't wake until the UFO disappeared. [ ]A. slept B. was sleeping C. was doing homework D. was singing …”主要考查了你对  【过去进行时】  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。