They can buy the pens a very good .A. at priceB. in priceC. at costD. at selling

问题补充：

They can buy the pens a very good .

A. at, price

B. in, price

C. at, cost

D. at, selling

答案：

(答案→)A. at, price

B. in, price

C. at, cost

D. at, selling

解析：固定搭配，以…价格at a…price。