D oxygen there was no free oxygen on the earth
In oxidation, oxygen is needed to create a chemical reaction.
Answer;
-NAD+
Explanation;
-When glucose breaks down into ATP, a large amount of the energy is stored as electron on special molecules (the electron carriers). When an empty electron carrier accepts a pair of electrons, it is reduced; when it gives those electrons up later on, it is oxidized.
-NAD+ and FAD; also the two most common electron carriers in the body. NAD+ can accept a pair of electrons (and a hydrogen ion) to become NADH.
