BOTH INTERNATIONAL & INLAND A fog signal of one short, one prolonged, and one short blast may be sounded by a __________.

Correct Answer: Option A — vessel at anchor

Under Inland Navigation Rules, for the condition where 'A fog signal of one short, one prolonged, and one short blast may be sounded by a', the correct requirement is: 'vessel at anchor'. This standard ensures clear navigational intent and collision avoidance.