A general form of equation of state for gases is $\mathrm{PV}=$ $\mathrm{RT}\left[\mathrm{A}+\mathrm{B} / \mathrm{V}+\mathrm{C} / \mathrm{V}^{2}+\ldots\right]$, where $\mathrm{V}$ is the molar
volume of the gas and $\mathrm{A}, \mathrm{B}, \mathrm{C} \ldots .$ are constants for the gas. The values of $\mathrm{A}$ and $\mathrm{B}$, if the gas obeys van der Waals equation, are respectively
(a) $1, \frac{a}{27 b}$
(b) $1, \mathrm{~b}-\frac{\mathrm{a}}{\mathrm{RT}}$
(c) $\frac{a}{R T}$
(d) $\frac{2 \mathrm{a}}{\mathrm{RT}}$