Answer: E) lactate ..NAD+
Step-by-step explanation:
In conditions of oxygen deprivation, cells can't undergo normal cellular respiration and must rely on other processes to obtain energy.
Muscle cells in particular, under anaerobic exercise, do not obtain enough oxygen to produce the energy needed and end up obtaining energy form a process different than cellular respiration: lactic fermentation.
Lactic fermentation turns a molecule of pyruvate into a molecule of lactate, at the same time it turns NADH into NAD+.