The Ratio of the Universe's Actual Density to the Critical $\rho _ { \text {critical } } \text {. }$

The ratio of the universe's actual density to the critical density is:

A) $\rho _ { \text {critical } } \text {. }$
B) $\pi / \rho$
C) $\Omega _ { 0 }$
D) H/D.
E) 1/H.