This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'In the stomach, H+ ions are secreted in exchange for \nSelect and explain. \nA. Na+, B. K+, C. Ca+, D. Cl-', 'role': 'user'}, {'content': 'Answer: B \nExplanation: H+-K+ ATPase is present in stomach.', 'role': 'assistant'}]