The equation for real gas is given by $$\left(P + \frac{a}{V^2}\right)(V - b) = RT$$, where P, V, T and R are the pressure, volume, temperature and gas constant, respectively. The dimension of $$ab^{-2}$$ is equivalent to that of:

A

Planck's constant

B

Compressibility

C

Strain

D

Energy density