BOTH INTERNATIONAL & INLAND Which signal may be used by a vessel that is in doubt as to whether sufficient action is being taken by another vessel to avoid collision?

Correct Answer: Option A — Five or more short rapid blasts on the whistle

Under Rule 34(d), when vessels in sight of one another are in doubt whether sufficient action is being taken to avoid collision, the vessel in doubt must immediately sound at least 5 short and rapid blasts on the whistle.