Two particles having mass ratio $n:1$ are interconnected by a light inextensible string that passes over a smooth pulley. If the system is released, then the acceleration of centre of mass of the system is

Question

$$\begin {array} {1 1} (a)\;(n-1)^2g & \quad (b)\;\bigg(\frac{n+1}{n-1}\bigg)^2 g \\ (c)\;\bigg(\frac{n-1}{n+1}\bigg)^2 g & \quad  (d)\;\bigg(\frac{n+1}{n-1}\bigg)g \end {array}$$