A solid spherical conductor has charge $+Q$ and radius $R.$ It is surrounded by a solid spherical shell

with charge $-Q,$ inner radius $2R,$ and outer radius $3R.$ Which of the following statements is true?

$($i$)$ The electric potential has a maximum magnitude at $C$ and the electric field has a maximum

magnitude at $A$

$($ii$)$ The electric potential has a maximum magnitude at $D$ and the electric field has a maximum

magnitude at $B.$

$($iii$)$ The electric potential at $A$ is zero and the electric field has a maximum magnitude at $D.$

$($iv$)$ Both the electric potential and electric field achieve a maximum magnitude at B$.$