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': 'Monochorionic monoamniotic twin occurs if division occurs : \nSelect and explain. \nA. Before 24 hours, B. 1-4 days, C. 4-8 days, D. > 8 days', 'role': 'user'}, {'content': 'Answer: D \nExplanation: > 8 days', 'role': 'assistant'}]