If the electric flux entering and leaving an enclosed surface respectively is $\phi_1$ and $\phi_2$, the electric charge inside the surface will be :
( A ) $(\phi_2 - \phi_1) \varepsilon_0$
( B ) $(\phi_1 + \phi_2)/ \varepsilon_0$
( C ) $(\phi_1 + \phi_2)\varepsilon_0$
( D ) $(\phi_2 - \phi_1)/ \varepsilon_0$