The formation of lactic acid in human muscles is closely associated with intense exertion or activity, during which aerobic respiration that uses oxygen to produce energy cannot be able to match the demand of energy by the muscles.
The muscles therefore resort to anaerobic respiration for energy where pyruvate becomes a makeshift hydrogen acceptor rather than oxygen as happens in aerobic respiration.
Pyruvate accepts a hydrogen from NADH and becomes reduced to lactate or lactic acid while NADH is oxidized to NAD
which is crucial in the formation of energy that is then stored in the form of ATP which is used to re-fuel the muscles to keep them going.
I would say Option B) because Option C) is wrong since matter cannot be created. A closed system does not exchange matter so it's not Option D). Since an island is an isolated area, Option A) is wrong.
