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: Unknown
[{'content': 'Which of the following predisposes to placenta previa? \nSelect and explain. \nA. Primigravida, B. Singleton pregnancy, C. Diabetesmellitus, D. Past cesarean pregnancy', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans: D', 'role': 'assistant'}]