----What can I do for you?--I’d like to buy a present for my teacher’s birthday at a

问题补充：

----What can I do for you?

----I’d like to buy a present for my teacher’s birthday, at a proper price, but of great value.

A. that

B. one

C. it

D. everything

答案：

A. that

(答案→)B. one

C. it

D. everything

解析：替代a+名词用one=a present,意思是：价格适合又很有价值的一份礼物。