$A$ dumbbell is placed in water of density $\rho$. It is observed that by attaching a mass $m$ to the rod,the dumbbell floats with the rod horizontal on the surface of water and each sphere exactly half submerged as shown in the figure. The volume of the mass $m$ is negligible. The value of length $l$ is

• A
  $\frac{d(\rho V - 3M)}{2(\rho V - 2M)}$
• B
  $\frac{d(\rho V - 2M)}{2(\rho V - 3M)}$
• C
  $\frac{d(\rho V + 2M)}{2(\rho V - 3M)}$
• D
  $\frac{d(\rho V - 2M)}{2(\rho V + 3M)}$