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: Microbiology
[{'content': 'Painless ulcer along with painless lymphadenopathy is characteristic of which STD: \nSelect and explain. \nA. Syphilis, B. Chancroid, C. LGV, D. Donovanosis', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is. 'a' i. e., Syphilis", 'role': 'assistant'}]