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

问题补充：

29．---- 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：考查连词的用法。这里起转折作用,while表示”但是”,可接句子.”前两个免费,但第三个要收费30元”