The correct answer is B. Lactic acid.
Lactic acid is a byproduct of anaerobic respiration, which is the process of producing energy without oxygen. When muscles are working hard, they need more energy than they can get from aerobic respiration. This causes them to switch to anaerobic respiration, which produces lactic acid as a byproduct.
Lactic acid can build up in the muscles, causing them to become sore and fatigued. This is why people often feel tired after exercise. The lactic acid will eventually be broken down by the body, but it can take some time.
Pyruvic acid is a molecule that is produced during glycolysis, which is the first step in the process of cellular respiration. Pyruvic acid can be converted into lactic acid or acetyl-CoA, which is used in the Krebs cycle.
Oxid acetic acid is a molecule that is produced during the Krebs cycle. It is a four-carbon molecule that is used to produce energy.
Uric acid is a waste product that is produced when the body breaks down purines. Purines are found in nucleic acids, which are the building blocks of DNA and RNA. Uric acid is excreted in the urine.
In conclusion, the muscle fatigue appears due the accumulation of lactic acid.