"Anaerobic process that restores NAD+ supply" describes the process of fermentation.
Answer: Option D
Step-by-step explanation:
"When oxygen is not present or an organism can not undergo aerobic respiration, pyruvate will be subjected to a process" called fermentation. These do not need oxygen, so is anaerobic. Also, will refill NAD+ formed in glycolysis from NADH + H+.
Although in humans, aerobic conditions generate pyruvate while anaerobic conditions go for lactate formation. There are two major kinds of anaerobic respiration involving alcoholic fermentation and fermentation of the lactic acid. These are not the preferred way to release the energy from the glucose molecules but it is the only alternative to survive when energy is needed.