--- 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
网友回答
(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。