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 is based on bohr's quantum model? model a model b model c model d