-I wonder how much you charge for your services-- The first two are free the thir

问题补充：

---- I wonder how much you charge for your services．

---- The first two are free the third costs $30．

A. while

B. until

C. when

D. before

答案：

(答案→)A. while

B. until

C. when

D. before

解析：考查连词用法。本题考查了while表示转折的用法，意为：然而；句意：—我想知道这服务你要收多少钱？—最先的两次免费，而第三次收费30。