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Serena , 18, sagged 6 in the second set tie breaker and closed with a double fault.
18岁的塞雷娜在第二盘的决胜局中士气低沉,终因发球双误败北.
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Double fault: A second failed serve in a row, resulting in the loss of the point.
双发失误: 连续两次发球失误, 造成失分.
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电话机双音频拨号集成电路原理及故障判断方法
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