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: Radiology
[{'content': 'First radiological sign in acute osteomyelitis is: \nSelect and explain. \nA. Soft tissue swelling, B. Periosteal reaction, C. Sequestrum, D. Involucrum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Soft tissue swelling', 'role': 'assistant'}]