A man aboard a vessel, signaling by raising and lowering his outstretched arms to each side, is indicating __________.

Correct Answer: Option C — a distress signal

COLREGS Annex IV explicitly designates the slow and repeated raising and lowering of arms outstretched to each side as an internationally recognized visual distress signal. This body language alerts observing mariners that the individual or vessel is in grave danger and requires immediate assistance.