The correct answer is D. All floating bodies are stable.
A. The center of buoyancy is located at the center of gravity of the displaced liquid. This is true because the buoyant force acts on the center of gravity of the displaced liquid.
B. For stability of a submerged body, the center of gravity of body must lie directly below the center of buoyancy. This is true because if the center of gravity is above the center of buoyancy, the body will be unstable and will overturn.
C. For stability of floating cylinders or spheres, the e.g. of body must lie below the center of buoyancy. This is true because if the center of gravity is above the center of buoyancy, the body will be unstable and will overturn.
D. All floating bodies are stable. This is not true because if the center of gravity is above the center of buoyancy, the body will be unstable and will overturn.