题目

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：A 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”

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