问题
选择题
| —When _________ the abacus _________? —In the sixth century by the Chinese people. |
A. is; invented B. did; invent C. was; invented D. does; invent |
答案
答案：C
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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 |
答案：C
