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 sign after radiation R,, is: \nSelect and explain. \nA. Erythema, B. Necrosis, C. Burns, D. Deep ulcer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Erythema', 'role': 'assistant'}]