In a region of space, the electric field is in the x-direction, proportional to x and given by $\overrightarrow{\mathrm{E}}=\mathrm{\alpha x}\widehat{\mathrm{i}}$, where $\alpha$ is a positive constant. Consider an imaginary cubical volume of edge a, with its edges parallel to the axes of coordinates. The charge inside this cubical volume is

• A

  ${\mathrm{\epsilon }}_0{\mathrm{\alpha a}}^3$

• B

  $\frac{{\mathrm{\alpha a}}^3}{{\mathrm{\epsilon }}_0}$

• C

  $\frac{1}{6}\left({\mathrm{\epsilon }}_0{\mathrm{\alpha a}}^2\right)$

• D

  zero