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 is caused by irradiation of: \nSelect and explain. \nA. Salivary glands, B. Enamel, C. Enamel and dentin, D. Oral mucosa', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]