BOTH INTERNATIONAL & INLAND At night, you see a vessel displaying the light shown in illustration D046RR below. This could be which of the following?

Correct Answer: Option A — sailing

COLREG Rule 25(a) requires sailing vessels underway to exhibit red and green sidelights along with a sternlight. Seeing these specific running lights without any masthead or towing lights conclusively identifies the vessel as operating under sail power alone during nighttime hours.