BOTH INTERNATIONAL & INLAND The use of the signal consisting of five or more short blasts on the ship's whistle __________.

Correct Answer: Option D — indicates doubt as to the other vessel's action

Under Inland Navigation Rules, for the condition where 'The use of the signal consisting of five or more short blasts on the ship's whistle', the correct requirement is: 'indicates doubt as to the other vessel's action'. This standard ensures clear navigational intent and collision avoidance.