An insulating hollow sphere has inner radius a and outer radius $b.$ Within the insulating material the volume charge density is given by $(r)=\frac{}{r},$ where $$ is a positive constant. In terms of $$ and $a,$ what is the magnitude of the electric field at a distance $r$ from the center of the shell, where $a\frac{1-(\frac{a}{r}{)}^2}{{}_0}2a\frac{1-(\frac{a}{r}{)}^2}{{}_0}a\frac{1-(\frac{a}{r}{)}^2}{2}{}_{0}a\frac{1-(\frac{a}{r}{)}^2}{4}{}_{0}a?$

$A.a\frac{1-(\frac{a}{r}{)}^2}{{}_0}$

$B.2a\frac{1-(\frac{a}{r}{)}^2}{{}_0}$

$C.a\frac{1-(\frac{a}{r}{)}^2}{2}{}_0$

$D.a\frac{1-(\frac{a}{r}{)}^2}{4}{}_0$