Answer: Option A
Explanation:
The aerobic respiration takes place inside the body when there is presence of oxygen in the body.
The product of aerobic respiration is carbon dioxide and water. This is a normal condition.
In case of exercises there is a lack of oxygen then anaerobic respiration takes place and end product of this respiration is ethyl alcohol and lactic acid.
The runner's muscle accumulate lactic acid in the muscles which causes pain.