People in China used to keep records by putting a number of stones together, ?
A. usedn’t they to
B. did they
C. used to they
D. didn’t they
网友回答
A. usedn’t they to
B. did they
C. used to they
(答案→)D. didn’t they
解析：反意问句中陈述部分谓语是used to ,是过去式，所以简短问句中要用didn't (they)。