Which is the correct statement?

• A

  For an isothermal change PV = constant

• B

  In an isothermal process the change in internal energy must be equal to the work done

• C

  For an adiabatic change  $\frac{{\mathrm{P}}_2}{{\mathrm{P}}_1}={\left(\frac{{\mathrm{V}}_2}{{\mathrm{V}}_1}\right)}^{\mathrm{\gamma }}$, where $\gamma$ is the ratio of specific heats

• D

  In an adiabatic process work done must be equal to the heat entering the system