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': 'Radiation caries appears in: \nSelect and explain. \nA. 3 weeks, B. 6 months, C. 3 months, D. 6 weeks', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]