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: Medicine
[{'content': 'Most common cause of sudden death \nSelect and explain. \nA. Ventricular fibrilation, B. Atrial fibrilation, C. PSVT, D. A-V block', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]