An ideal gas undergoes a quasi-static,reversible process in which its molar heat capacity $C$ remains constant. If during this process the relation of pressure $P$ and volume $V$ is given by $PV^n = \text{constant}$,then $n$ is given by (Here $C_p$ and $C_v$ are molar specific heat at constant pressure and constant volume,respectively):

• A
  $n = \frac{C_p - C}{C - C_v}$
• B
  $n = \frac{C - C_v}{C - C_p}$
• C
  $n = \frac{C_p}{C_v}$
• D
  $n = \frac{C - C_p}{C - C_v}$