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': '100 women, followed up for 20 months, with OCPs, 5 became pregnant. Calculate the Pearl Index \nSelect and explain. \nA. 1, B. 2, C. 3, D. 4', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]