Answer:
Option A,C
Explanation:
Option (a) is correct due to symmetry.
Option (b) is wrong again due to symmetry.
Option (c) is correct because as per Gauss's theorem, net electric flux passing through any closed surface = $\frac{q_{in}}{\varepsilon_{0}}$
here, $q_{in}=3q-q-q=q$
$\therefore$ Net electric flux=$\frac{q}{\varepsilon_{0}}$
Option (d) is wrong because there is no symmetry in two given planes