◎ 题干
——Why is the classroom so dirty?
——Sorry, Sir. It _____ yesterday. We forgot to do it.
A.doesn't cleanB.didn't cleanC.isn't cleanedD.wasn't 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“——Why is the classroom so dirty?——Sorry, Sir. It _____ yesterday. We forgot to do it.A.doesn't cleanB.didn't cleanC.isn't cleanedD.wasn't 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。