Correct Answer: C

Rationale: The kidneys are the organs responsible for filtering blood, removing waste products, and regulating fluid and electrolyte balance. Each kidney contains about one million nephrons — microscopic filtration units that process around 180 liters of blood daily. The kidneys maintain homeostasis by controlling water balance, pH, and salt levels while excreting urea and other toxins through urine. They also produce hormones like erythropoietin, which stimulates red blood cell production. Proper kidney function is crucial for maintaining overall health, and impairment can lead to conditions such as hypertension or renal failure.

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