BOTH INTERNATIONAL & INLAND You are underway, in fog, when you hear a whistle signal of one prolonged blast followed by two short blasts. This signal could indicate a vessel __________.

Correct Answer: Option C — not under command

Under Inland Navigation Rules, for the condition where 'You are underway, in fog, when you hear a whistle signal of one prolonged blast followed by two short blasts. This signal could indicate a vessel', the correct requirement is: 'not under command'. This standard ensures clear navigational intent and collision avoidance.