If the ratio of specific heat of a gas at Constant pressure to that at constant volume is $\gamma$, the Change in internal energy of the mass of gas, when the volume changes from $\mathrm{V}$ to $2 \mathrm{~V}$ at Constant Pressure p, is
(A) $\{(\mathrm{PV}) /(\gamma-1)\}$
(B) $\{\mathrm{R} /(\gamma-1)\}$
(C) PV
(D) $\{(\gamma \mathrm{PV}) /(\gamma-1)\}$