A material has density $\rho$ and bulk modulus $k$. The increase in the density of the material when it is subjected to an external pressure $P$ from all sides is
(a) $\frac{P}{\rho k}$
(b) $\frac{k}{\rho P}$
(c) $\frac{\rho P}{k}$
(d) $\frac{\rho k}{P}$