Solve this:

Q. Two isolated point masses m and M are separated by a distance $\mathcal{l}$. The moment of inertia of the system about an axis passing through a point where gravitational field is zero and perpendicular to the line joining the two masses, is 

     $$\begin{gathered} \left(\mathrm{A}\right) \frac{{\mathrm{m}}^2 +{\mathrm{M}}^2}{{\left(\sqrt{\mathrm{m}} +\sqrt{\mathrm{M}}\right)}^2}{\mathcal{l}}^2 \left(\mathrm{B}\right) \frac{\mathrm{m} +\mathrm{M}}{\left(\sqrt{\mathrm{m}} +\sqrt{\mathrm{M}}\right)}{\mathcal{l}}^2 \\ \left(\mathrm{C}\right) \frac{\mathrm{m} +\mathrm{M}}{{\left(\sqrt{\mathrm{m}} +\sqrt{\mathrm{M}}\right)}^2}{\mathcal{l}}^2 \left(\mathrm{D}\right) \mathrm{none} \mathrm{of} \mathrm{the} \mathrm{above} \end{gathered}$$