The correct answer is: D. none of the above
The position of the center of pressure on a plane surface immersed vertically in a static mass of fluid depends on the shape of the surface and the density of the fluid. In general, the center of pressure is located below the centroid of the submerged area, but it can be above or below the centroid depending on the shape of the surface.
For a flat plate, the center of pressure is located at one-third of the depth of the plate below the free surface. For a curved surface, the center of pressure is located at a point that is a function of the shape of the surface and the density of the fluid.
The center of pressure is important because it is the point at which the total force of the fluid on the surface acts. This force can be used to calculate the stresses on the surface and to design structures that can withstand the forces of the fluid.