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You are Master of a towing vessel engaged in towing three barges astern.The middle barge of the tow would be required to sound which of the following during restricted visibility （）.
A:No fog signal
B:A prolonged blast at intervals never to exceed more than two minutes
C:A prolonged blast followed by two short blasts at intervals never to exceed more than two minutes
D:A prolonged blast followed by three short blasts at intervals never to exceed more than one minute

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出自：海船船员证

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