The correct answer is D. all of the above.
A floating body is in equilibrium when the sum of all the forces acting on it is zero. This means that the weight of the body must be equal to the buoyant force acting on it. The buoyant force is equal to the weight of the fluid displaced by the body.
The metacenter is a point located above the center of buoyancy. It is the point about which the body will rotate if it is disturbed. The metacenter must be above the center of buoyancy for the body to be in stable equilibrium.
A righting couple is a force couple that acts to return the body to its original position if it is disturbed. The righting couple is created by the difference in the vertical forces acting on the two sides of the body.
If any of the conditions above are not met, the body will not be in equilibrium and will either sink or capsize.