This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'Hyperpolarization is caused by which ions \nSelect and explain. \nA. K+, B. Na+, C. Ca++, D. HCO3', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Slow return of the K+ channels to the closed state causing hyperpolarization.(Ref Textbook of physiology AK Jain 5th edition page no.36)', 'role': 'assistant'}]