--What can I do for you?--I am looking for a birthday gift for my sister at a proper pric

问题补充：

--What can I do for you?

--I am looking for a birthday gift for my sister, at a proper price but fashionable.

A. one

B. anyone

C. that

D. everything

答案：

(答案→)A. one

B. anyone

C. that

D. everything

解析：考查同位语。本题中的one与前句的a birthday gift是同位语从句，指一个…的礼物；句意：—我能为你做什么吗？—我正在为我的姐姐找一个礼物，一个价格很合适也很时尚的礼物。故A正确。