In the IALA Buoyage System, preferred-channel-to-port or preferred-channel-to-starboard buoys, when fitted with lights, will show a __________.

Correct Answer: Option C — composite group flashing (2 + 1) light

IALA preferred-channel buoys feature a distinctive composite group flashing (2 + 1) light rhythm. This unique characteristic differentiates them from standard starboard and port lateral marks, providing mariners unambiguous nighttime identification when approaching bifurcations or channel junctions.