BOTH INTERNATIONAL & INLAND While underway in fog you hear a whistle signal consisting of one prolonged blast followed immediately by two short blasts. This signal is sounded in fog by __________.

Correct Answer: Option B — vessels underway and towing

Under Inland Navigation Rules, for the condition where 'While underway in fog you hear a whistle signal consisting of one prolonged blast followed immediately by two short blasts. This signal is sounded in fog by', the correct requirement is: 'vessels underway and towing'. This standard ensures clear navigational intent and collision avoidance.