A nurse is caring for a client who is at risk for metabolic acidosis. Which mechanism should the nurse identify as the first line of defense against changes in the pH of the blood?

Rationale: A. Acids contribute to pH changes but do not defend against them. B. Chemical buffers are the first line of defense; they react immediately to neutralize excess acids or bases and help maintain pH balance. C. The respiratory system is the second line of defense, adjusting CO₂ levels to influence pH. D. The renal system is the third line of defense, regulating acid-base balance by excreting hydrogen ions and reabsorbing bicarbonate, but it acts more slowly.