# During an adiabatic process, if the pressure of an ideal gas is proportional to the cube of its temperature the ratio $\gamma = \frac{c_p}{c_v}$ is : <br> (Specific heat at constant volume = $c_v$ <br> specific heat at constant pressure = $c_p$ )
( A ) $\frac{3}{2}$
( B ) $\frac{1}{5}$
( C ) $\frac{4}{3}$
( D ) $\frac{5}{3}$