At a High Temperature, Carbon Dioxide Decomposes to Produce Carbon $\leftrightarrows$

At a high temperature, carbon dioxide decomposes to produce carbon monoxide and oxygen. When equilibrium is established, which, if any, of the following ratios is constant and independent of the initial concentration of carbon dioxide and whether or not oxygen was present initially?
CO₂(g) $\leftrightarrows$ CO(g) +1/2 O₂(g)

A) $\frac { \left[ \mathrm { CO } _ { 2 } \right] } { [ \mathrm { CO } ] \left[ \mathrm { O } _ { 2 } \right] }$
B) $\frac { \left[ \mathrm { CO } _ { 3 } \right] \left[ \mathrm { O } _ { 2 } \right] } { \left[ \mathrm { CO } _ { 2 } \right] }$
C) $\frac { [ \mathrm { CO } ] \left[ \frac { 1 } { 2 } \mathrm { O } _ { 2 } \right] } { \left[ \mathrm { CO } _ { 2 } \right] }$
D) $\frac { \left[ \mathrm { CO } ^ { 2 } \left[ \mathrm { O } _ { 2 } \right] \right. } { \left[ \mathrm { CO } _ { 2 } \right] ^ { 2 } }$
E) None of these ratios correctly describes the equilibrium concentrations.