It Is Easier to Significantly Alter the Earth's CO₂ balance

It is easier to significantly alter the earth's CO₂ balance than its O₂ balance because

A) CO₂ is a very unstable molecule whereas O₂ is stable.
B) CO₂ is a trace molecule in the atmosphere whereas O₂ is not.
C) it is so much easier to produce CO₂.
D) CO₂ is a highly reactive molecule whereas O₂ is inert.
E) CO₂ is an inert molecule whereas O₂ is highly reactive.