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': 'Contraceptive efficacy is assessed by ? \nSelect and explain. \nA. Pearl index, B. Chandelers index, C. Quetlet index, D. Broca index', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Pearl index", 'role': 'assistant'}]