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 ulcers are characteristically painless \nSelect and explain. \nA. Trauma, B. Tuberculosis, C. Primary syphilis, D. Herpes', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]