问题补充：
－?
－Yes, I’d like to buy some milk.
A. What can I do for you
B. Can I help you
C. Can you help me
D. What do you want
答案：
A. What can I do for you
(答案→)B. Can I help you
C. Can you help me
D. What do you want
解析：What can I do for you能为您做点什么；Can I help you需要帮忙吗？Can you help me你能帮助我吗？What do you want你想要什么。根据下文答语，是的我想买牛奶。选项B是比较通用的服务用语，故选B。
