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': 'Plateau phase of action potential of cardiac muscle starts with \nSelect and explain. \nA. Inactivation of Na+ channel, B. Entry of Ca2+, C. Opening of K+ channel, D. Closure of K+ channel', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Plateau phase (Phase 2) starts with entry of Ca2+\nCa2+\xa0entry is counterbalanced by efflux of K+. Hence, Plateau is maintained.', 'role': 'assistant'}]