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': 'Best treatment of old fracture is \nSelect and explain. \nA. Manipulation and POP cast application., B. Open reduction and internal fixation and bone grafting., C. K Wire fixation, D. External fixation', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Nonunion fracture shaft femur requires open reduction and rigid internal fixation with either intramedullary nail or DC plating and bone grafting.', 'role': 'assistant'}]