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 D — composite group flashing (2 + 1) light

IALA preferred-channel marks are laterally marked with red and green horizontal bands. When lighted, they utilize a composite group flashing (2 + 1) characteristic. This distinct rhythm allows mariners to identify the mark as a junction buoy, indicating the primary channel direction based on the color of the topmost band.