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': 'Sourse of progesterone during normal mestrual cycle : \nSelect and explain. \nA. Corpus luteum, B. Stroma, C. Surface epithelium of ovary, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Corpus luteum', 'role': 'assistant'}]