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
Which of the following ulcers are characteristically painless 
Select and explain. 
A. Trauma, B. Tuberculosis, C. Primary syphilis, D. Herpes
C: Primary syphilis
Answer: C: Primary syphilis 
Explanation: None