BOTH INTERNATIONAL & INLAND What signal indicates doubt that sufficient action is being taken by another vessel to avoid collision?

Correct Answer: Option D — Five short and rapid blasts of the whistle

Rule 34(d) defines the danger signal as at least five short and rapid blasts on the whistle. This signal is mandatory when a vessel is in doubt regarding the intentions or actions of another vessel in sight, serving as a critical warning to prevent a potential collision situation.