In small-angle stability, when external forces exist, the buoyant force is assumed to act vertically upwards through the center of buoyancy and through the __________.

Correct Answer: Option A — metacenter

In small-angle stability, the metacenter (M) is the intersection of the vertical line through the center of buoyancy and the initial centerline. For small angles of heel, the buoyant force acts through this point, allowing the metacentric height (GM) to serve as a reliable indicator of the vessel's initial transverse stability.