What is the flux through a cube of side 'a' if a point charge of q is at one of its corner.

Question

( A ) $\frac{q}{\epsilon_0}$
( B ) $\frac{q}{2\epsilon_0}6a^2$
( C ) $\frac{q}{8\epsilon_0}$
( D ) $\frac{2q}{\epsilon_0}$