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': 'Magnitude of action potential is determined by: \nSelect and explain. \nA. Na+, B. Mg++, C. K++, D. Ca++', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Maximum\xa0magnitude\xa0is\xa0determined\xa0by equilibrium potential of Na+\xa0ion.', 'role': 'assistant'}]