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': 'Causes of antepaum hemorrhage are all except \nSelect and explain. \nA. Placenta pre, B. Atonic uterus, C. Abruptio placenta, D. Circumvallate placenta', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Atonic uterus', 'role': 'assistant'}]