A、＄15. B、＄12. C、＄21. D、＄9. D题目询问男士买玫瑰花费多少钱。由女士的话可知玫瑰花的价格是“...a half for each red rose”，男士说“I’d like...half a dozen red roses．”因此

M: How much are the carnations and tile roses?
W: One dollar for each carnation and (9)one and a half for each red rose.
M: (9)Then I’d like a dozen red carnations and half a dozen red roses.
W: I bet it’s for your mother, (8)as it’s Mother’s Day today.
M: Well, not completely true. (8)It happens to be her birthday.
W: Oh, really? I guess she must be very happy to receive these beautiful carnations from you.
M: Yeah, she will. She really likes flowers. So I buy her some every year. I’d just wish they would stay fresh longer than they do.
W: (10)Put a little sugar and vitamin C in the water. They’ll stay fresh for days.
M: Really? I’ll tell my mother. And thanks for your suggestion.
W: That’s all right. Happy birthday to your mother!