The diagram shows the different models of the atom that eventually led to the modern atomic theory. Four diagrams are shown labeled Model A, Model B, Model C, Model D from left to right. The diagram labeled Model A has a small sphere with a positive sign on it. This small sphere at the center is surrounded by a shaded circle. The shaded circle has negative signs placed randomly inside it. The diagram labeled Model B is a large solid sphere. The diagram labeled Model C has a sphere at the center and a dotted cloud around the sphere. The dotted cloud is dense near the sphere and becomes faint as we move away from the sphere. The diagram labeled Model D has a sphere surrounded by three concentric circles. Each concentric circle has some spheres on it.

Which model represents the current atomic theory based on our knowledge of the nucleus and electron cloud?