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: Social & Preventive Medicine
[{'content': 'Best index for measuring efficacy of contraception is, \nSelect and explain. \nA. Pearl Index, B. Life Table Analysis, C. Couple protection rate, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]