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: Surgery
[{'content': 'Commonest site of fracture leading to fat-embolism is: \nSelect and explain. \nA. Tibia, B. Femur, C. Humerus, D. Ulna', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Femur', 'role': 'assistant'}]