A coaxial cable has the cross section shown in the figure. The shaded region is insulated. The regions in which r < a and b < r < c are conducting. A uniform dc current density of total current I flows along the inner part of the cable (r < a) and returns along the outer part of the cable ( b< r < c) in the directions shown. The radial dependence of the magnitude of the magnetic field, H, is shown by which of the following?