问题
选择题
— 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
答案：D
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— 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：D