A thermodynamic system undergoes a cyclic process ABCDA as shown in figure. The work done by the system is 

 

• A

  ${\mathrm{P}}_0{\mathrm{V}}_0$

• B

  $2{\mathrm{P}}_0{\mathrm{V}}_0$

• C

  $\frac{{\mathrm{P}}_0{\mathrm{V}}_0}{2}$

• D

  Zero