KVPY SX SB Exam 2013 Question Paper

The equation of state of n moles of a non-ideal gas can be approximated by the equation
$\left(\mathit{P}+\frac{{\mathrm{n}}^2\mathrm{a}}{{\mathrm{V}}^2}\right)\left(\mathrm{V}-\mathrm{nb}\right)=\mathrm{nRT}$
where a and b are constants characteristic of the gas. Which of the following can represent the equation of a quasistatic adiabat for this gas (Assume that ${\mathrm{C}}_{\mathrm{V}}$, the molar heat capacity at constant volume, is independent of temperature) ?