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
Treponema pallidum isolation from CSF is maximum in which stage of syphilis? 
Select and explain. 
A. Primary syphilis, B. Secondary syphilis, C. Teiary syphilis, D. Tabes dorsalis
B: Secondary syphilis
Answer: B: Secondary syphilis 
Explanation: B. i.e. Secondary syphilis