---- 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
网友回答
(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。