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': 'Menstruation occurring every 15 daysis : \nSelect and explain. \nA. Polymenorrhea, B. Epimenorrhea, C. Cryptomenorrhea, D. Hypomenorrhea', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Polymenorrhea', 'role': 'assistant'}]