
$V(z)\, = \,30 - 5{z^2}for\,\left| z \right| \le 1\,m$
$V(z)\, = \,35 - 10\,\left| z \right|for\,\left| z \right| \ge 1\,m$
$V(z)$ does not depend on $x$ and $y.$ If this potential is generated by a constant charge per unit volume $\rho _0$ (in units of $\varepsilon _0$ ) which is spread over a certain region, then choose the correct statement

$A$. the charge stored in it, increases.
$B$. the energy stored in it, decreases.
$C$. its capacitance increases.
$D$. the ratio of charge to its potential remains the same.
$E$. the product of charge and voltage increases.
Choose the most appropriate answer from the options given below:

