摘要： --When the abacus ? -- In the sixth century by the Chinese people. A. is, invented B. did, invent C. was, invented D. does, invent
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--When _____ the abacus _____? -- In the sixth century by the Chinese people.
|
A．is, invented |
B．did, invent |
C．was, invented |
D．does, invent |
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