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': 'Antigenic variation is/are seen in-a) Treponema pallidumb) Neisseriac) Corynebacteriumd) Borrelia recurrentis \nSelect and explain. \nA. bd, B. d, C. ab, D. ac', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]