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': 'Primary amenorrhea is when : \nSelect and explain. \nA. Menstruation does not occur even after 18 year, B. Menstruation does not occur even after 15 year of age, C. Imperforate hymen exists, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Menstruation does not occur even after 15 year of age', 'role': 'assistant'}]