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': "'Canker sore' is otherwise commonly known as \nSelect and explain. \nA. Recurrent apthous ulcer, B. Recurrent herpetic gingivitis, C. Acute necrotizing ulcerative gingivitis, D. Recurrent herpes labialis", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]