This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal physiology, Subject name: Physiology
[{'content': 'The function of P cells of the kidney is \nSelect and explain. \nA. H+ secretion, B. K+ reabsorption, C. Na+ reabsorption, D. Cl- secretion', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The principal cells reabsorb sodium and water from the lumen and secrete potassium ions into the lumen.', 'role': 'assistant'}]