Oxidation is a favorable process in an aerobic environment, which is the reason cells are able to derive energy from the oxidation of macromolecules. Once carbon has been oxidized to _______________, its most stable form, it can only cycle back into the organic portion of the carbon cycle through _______.
(a) CO2, photosynthesis.
(b) CH3, combustion.
(c) CO2, respiration.
(d) CO, reduction.
Answer: A