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': 'Simple hyperplasia of the endometrium treated with progesterone for-- days : \nSelect and explain. \nA. 14, B. 21, C. 5, D. 10', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 21', 'role': 'assistant'}]