This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oral cavity, Subject name: Surgery
[{'content': 'A patient has small, oval multiple ulcers in oral cavity with red erythematous margins. The diagnosis is: \nSelect and explain. \nA. Carcinoma, B. Tubercular ulcer, C. Aphthous ulcer, D. Syphilitic ulcer', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Aphthous ulcer Small and oval multiple ulcers in oral cavity Has red erythematous margins Syphilitic ulcer Firm, painless, non-itchy skin ulceration Tubercular ulcer Firm, nontender erythematous nodules that soften, ulcerate, and form sinuses.', 'role': 'assistant'}]