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': 'Bleeding associated with anovulation is due to \nSelect and explain. \nA. Persistent proliferative endometrium., B. Alterations in endometrial vascular structure., C. Increased endometrial responsiveness to vasodilating prostaglandins., D. Impaired prostaglandins concentration.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: As ovulation does not occur, proliferative endometrium persists causing bleeding.', 'role': 'assistant'}]