Question

【题目】— Do you know _______?
— In the 6th century.
A.when is the abacus invented
B.when the abacus is invented
C.when was the abacus invented
D.when the abacus was invented

Answer 1

【答案】D
【解析】考查宾语从句。宾语从句应用陈述语序，排除A、C两项，由答句In the 6th century. 可知，问句用过去时。所以答案是D