INTERNATIONAL ONLY Two power-driven vessels are crossing within one half mile of each other as shown in illustration D042RR below. Vessel "A" sounds one short blast of the whistle. What signal should vessel "B" sound?

Correct Answer: Option D — None of the above

COLREGS Rule 34(a) mandates that whistle signals are only used when vessels are in sight of one another and are actively altering course. Because the vessels are merely crossing without an indicated maneuver, no signal is required or permitted. Therefore, the correct response is that no signal should be sounded.