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: Skin
[{'content': 'Treponema pallidum isolation from CSF is maximum in which stage of syphilis? \nSelect and explain. \nA. Primary syphilis, B. Secondary syphilis, C. Teiary syphilis, D. Tabes dorsalis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B. i.e. Secondary syphilis', 'role': 'assistant'}]