◎ 题干
When the teacher came into the classroom, all of us __________ the classroom.
A. are cleaning   
B. were cleaning   
C. cleaned
D are  cleaned
◎ 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 the teacher came into the classroom, all of us __________ the classroom.A. are cleaningB. were cleaningC. cleanedDare cleaned…”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。