-are stamps used ?--Sending letters.A. Why forB. What forC. What /D. How for

问题补充：

---- are stamps used ? ----Sending letters.

A. Why, for

B. What, for

C. What, /

D. How, for

答案：

A. Why, for

(答案→)B. What, for

C. What, /

D. How, for

解析：句意：---邮票被用于做什么？---寄信。what……for 为了……，表示目的。故选B。