问题补充：
—What can I do for you?
—I’d like to buy a computer for my son, at a good price but of great quality．
A. that
B. one
C. which
D. the one
答案：
A. that
(答案→)B. one
C. which
D. the one
解析：考查one和 the one的用法，one表示代替前面提到的名词；the one表示特指代替前面提到的名词，句子意思“我想给儿子买台电脑，一个好的价钱并且质量好的电脑”，所以选B
