This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
[{'content': 'Antigenic variation seen in which of the following - \nSelect and explain. \nA. Influenza virus, B. Hepatitis virus, C. Yellow fever virus, D. Leptospira', 'role': 'user'}, {'content': 'Answer: A \nExplanation: a unique feature of influenza virus ability to undergo antigenic variation REF:MICROBIOLOGY ANANTHA NARAYANAN NINTH EDITION PAGE.499', 'role': 'assistant'}]