—Good luck with your new diet Ricky.— A. Thanks Millie.B. You’re welcome.C. My pleasure.

问题补充：

—Good luck with your new diet, Ricky.

—

A. Thanks, Millie.

B. You’re welcome.

C. My pleasure.

D. Oh, really？

答案：

(答案→)A. Thanks, Millie.

B. You’re welcome.

C. My pleasure.

D. Oh, really？

解析：在英文中，当别人对你表示祝愿的话应该表示感谢说thanks，故本题选A。