Four spheres each of mass \( m \) form a square of side \( d \) (as shown in figure). A fifth sphere of mass \( M \) is situated at the centre of square. The total gravitational potential energy of the system is:
\( - \dfrac{G m}{d} \left[ (4 + \sqrt{2}) m + 4 \sqrt{2} M \right] \)
\( - \dfrac{G m}{d} \left[ (4 + \sqrt{2}) M + 4 \sqrt{2} m \right] \)
\( - \dfrac{G m}{d} \left[ 3 m^{2} + 4 \sqrt{2} M \right] \)
\( - \dfrac{G m}{d} \left[ 6 m^{2} + 4 \sqrt{2} M \right] \)