c
In the given cyclic process, From $A$ to $B$, the pressure is constant.
From $C$ to $A, P \propto T$
Hence, the volume is constant.
From $B$ to $C$, the temperature is constant.
Hence, $P \propto \frac{1}{V}$
From $C$ to $A,$ volume is constant.
Hence, when presented on $P V,$ it would be represented by option $\mathrm{C}$.