PTT信号在语音通信交换系统内部是当成语音信号进行处理的。
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A vessel may exhibit lights other than those prescribed by the Rules as long as the additional lights（）.
A. are not the same color as either side light
B. have a lesser range of visibility than the prescribed lights
C. do not impair the visibility or distinctive character of the prescribed lights
D. All of the above
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