◎ 题干
- Do you know       ?       
- In the 6th century.
[     ]
A. who is the abacus invented
B. when the abacus is invented
C. when was the abacus invented
D. when the abacus was invented
◎ 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“—Do you know ?— In the 6th century.[ ]A. who is the abacus invented B. when the abacus is inventedC. when was the abacus inventedD. when the abacus was inv…”主要考查了你对  【宾语从句】  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。