I wonder how much you charge for your serviceThe first two are free the third c

问题补充：

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

--- 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。While 意为然而，表对比， until直到 when当……时候 before在之前

句意为，---我想知道你的服务要收多少钱？

-----前面两个免费，然而第三个要三十美元。