A) a large amount of oxygen has been used AND a small amount of degradable organic matter is present. B) a small amount of oxygen has been used AND a large amount of degradable organic matter is present. C) a large amount of degradable organic matter is present AND a small number of viruses are present. D) a small number of viruses are present AND a large amount of oxygen has been used. E) a large amount of oxygen has been used AND a large amount of degradable organic matter is present.