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: Gynaecology & Obstetrics
[{'content': 'Pearl Index is a measure of : \nSelect and explain. \nA. Potency of contraceptives, B. Feility rate, C. Potency of disinfectant, D. Couple protection rate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Potency of contraceptives', 'role': 'assistant'}]