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': 'Which of the following is a painful ulcer? \nSelect and explain. \nA. syphilitic ulcer, B. trophic ulcer, C. oral chancre, D. all the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]