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': 'Red or brown discoloration of teeth is seen in \nSelect and explain. \nA. Porphyra, B. Internal resorption, C. Nasmynth membrane, D. Silver', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]