--What can I do for you?
-- I’d like to buy a present for my son, at a proper price but of great use.
A. one
B. the one
C. which
D. that
网友回答
(答案→)A. one
B. the one
C. which
D. that
解析：考查代词：分析句子结构：后半句 “at a proper price but of great use” 没有动词，不是一个完整的句子，所以不选连接词which 和 it，而one可以做代词，指代a present，the one有特指的意思，这里还没有选好礼物，不用特指。选C。