不能通过系统刷通行证验证的“广东省公安机关特殊工作车辆通行证”为无效通行证，收费员应拒绝给予免费放行。
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Acknowledgement by you of receipt of a distress message from a vessel which，beyond any possible doubt，is not in your vicinity and is a long distance away must be made when（）.
A. Vessels nearer the distress vessel acknowledge receipt
B. Vessels nearer the distress vessel fail to acknowledge receipt
C. Even you have not reveived the distress
D. Even the vessel in distress expressly prohibit you from providing any salvage service
光路接头及各点损耗中ODF损耗：（）。
A. 1dB
B. 2dB
C. 3dB
D. 4dB
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