Three body systems work at different speeds to keep the pH in the narrow range of normal, The order of effectiveness for these three systems is:

Rationale: A. Kidneys are the slowest to respond, so this order is incorrect. B. Kidneys are slower than lungs, so this order is incorrect. C. Lungs respond faster than kidneys but slower than chemical buffers, so this order is incorrect. D. Chemical buffers act immediately to neutralize pH changes (first line), lungs adjust CO₂ levels within minutes (second line), and kidneys regulate acid-base balance over hours to days (third line), making this the correct order.