The pulley shown in the figure is made using a thin rim and two rods of length equal to the diameter of the rim. The rim and each rod have a mass of $M$. Two blocks of mass $M$ and $m$ are attached to two ends of a light string passing over the pulley,which is hinged to rotate freely in a vertical plane about its centre. The magnitude of the acceleration experienced by the blocks is . . . . . . (assume no slipping of the string on the pulley.)

• A
  $\frac{(M-m) g}{\left[\left(\frac{13}{6}\right) M+m\right]}$
• B
  $\frac{( M - m ) g }{ M + m }$
• C
  $\frac{( M - m ) g }{\left[\left(\frac{8}{3}\right) M + m \right]}$
• D
  $\frac{( M - m ) g }{2 M + m }$