In the P-V diagram shown in figure ABC is a semicircle. The work done in the process ABC is

• A

  zero

• B

  $\frac{\mathrm{\pi }}{2}\mathrm{atm}-\mathrm{\ell }$

• C

  $-\frac{\mathrm{\pi }}{2}\mathrm{atm}-\mathrm{\ell }$

• D

  $4\mathrm{atm}-\mathrm{\ell }$