Excess Nitrates in the water supply
The answer is letter A. In most organisms cellular respiration usually involves oxygen to produce the most energy. Except in the process of fermentation, where the cells are deprived with oxygen causing it to form bacteria and other forms of organisms within the fermented sample.
The answer is iron. Research has shown an increase in serum iron concentreation in athletes and a concomitant decrease in magnesium ions. The increase in iron concentration is thought to be attributed to tissue injury from the strenuous physical activity. The decrease in magnesium is due to demand by the skeletal muscles.