Four sphere of diameter 2a and mass M are placed with their centres of the four comers of a square of side b. Then the moment of inertia of the system about an axis along one of the sides of the square is

• A

  $\frac{4}{5}{\mathrm{Ma}}^2+2{\mathrm{Mb}}^2$

• B

  $\frac{8}{5}{\mathrm{Ma}}^2+2{\mathrm{Mb}}^2$

• C

  $\frac{8}{5}{\mathrm{Ma}}^2$

• D

  $\frac{4}{5}{\mathrm{Ma}}^2+4{\mathrm{Mb}}^2$