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: Pathology
[{'content': 'Tetracycline stains appear as: \nSelect and explain. \nA. Yellow and brown stains in enamel and dentin, B. Yellow and brown stains only in enamel, C. Yellow and brown stains only in dentin, D. Only yellow stain in enamel', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]