问题
选择题
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
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”
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