ANS:C - metacentre.

A slight displacement of a floating body in a liquid causes it to oscillate about its metacentre. The metacentre is a point in a floating body where the buoyant force intersects the body's centerline. It is an important parameter in stability analysis of floating bodies. When a floating body undergoes a small angular displacement, it experiences a restoring moment that tends to return it to its original position. This restoring moment is caused by the shifting of the center of buoyancy, and the metacentre is the point around which this restoring moment acts. Therefore, the correct answer is: metacentre.