题干
—— What can I do for you?
——I’d like to buy a gift for my mother’s birthday, one at _________ proper price but of ___________ use and it’d better be __________ surprise.
——I’d like to buy a gift for my mother’s birthday, one at _________ proper price but of ___________ use and it’d better be __________ surprise.
A：the; /; a
B：the; a ; /
C：a; the; /
D：a; / ; a
答案(点此获取答案解析）
D
满足
，且
，
，
成等差数列，则此数列的公比等于 ( )