The center of buoyancy and the metacenter are in the line of action of the buoyant force __________.

Correct Answer: Option D — at all times

The center of buoyancy (B) and the metacenter (M) always lie on the vertical line of action of the buoyant force. This geometric relationship holds true regardless of the vessel's stability condition, as the buoyant force acts vertically through the center of the displaced volume at all times.