A long round conductor of cross-sectional area $A$is made of a material whose resistivity depends on the radial distance $r$ from the axis of a conductor as $\rho =\frac{\lambda }{r^2},\lambda$ is a constant. The total resistance per unit length of the conductor is $R$ and the electric field strength in the conductor due to which a current $I$ flows in it is $E$, then

I. $R=\frac{\pi \lambda }{A^2}$         II. $R=\frac{2\pi \lambda }{A^2}$        III.$E=\frac{\pi \lambda I}{A^2}$          IV.$E=\frac{2\pi \lambda I}{A^2}$