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': 'Stain for treponema \nSelect and explain. \nA. Fontanas method, B. Acid fast, C. Methenamine silver, D. PAS', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]