Correct Answer - d
Lactic acid produced in the muscle from the metabolism of carbohydrate in the cells . When muscles work hard (as during the time of exercise), the ament of `O_(2)` needded is used during energy production . Thus `O_(2)` lacks in the muscles.
This results to another process called anauobic metabolism. The product of this process of obtaining energy by anaerobically is lactic acid which is build up in muscles and caused pain. However , lactic acid produced helps in healing process actually.
