The molar specific heats of an ideal gas at constant pressure and constant volume are denoted by $C_p$ and $C_v$ respectively. If $\gamma = \frac{C_p}{C_v}$ and $R$ is the universal gas constant,then $C_v$ is equal to:

• A
  $\frac{1 + \gamma}{1 - \gamma}$
• B
  $\frac{R}{\gamma - 1}$
• C
  $\frac{\gamma - 1}{R}$
• D
  $\gamma R$