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': 'Which of the following has LEAST pregnancy failure rate : \nSelect and explain. \nA. OCP, B. IUCD, C. Diaphragm, D. Condom', 'role': 'user'}, {'content': 'Answer: A \nExplanation: OCP', 'role': 'assistant'}]