b
(b) ${W_{AB}}$ is negative (volume is decreasing) and
${W_{BC}}$ is positive (volume is increasing) and
since, $\left| {\,{W_{BC}}} \right|\, > \,\left| {\,{W_{AB}}} \right|$
$\therefore $ net work done is positive and area between semicircle which is equal to $\frac{\pi }{2}atm - lt.$