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
Antigenic variation seen in which of the following - 
Select and explain. 
A. Influenza virus, B. Hepatitis virus, C. Yellow fever virus, D. Leptospira
A: Influenza virus
Answer: A: Influenza virus 
Explanation: a unique feature of influenza virus ability to undergo antigenic variation REF:MICROBIOLOGY ANANTHA NARAYANAN NINTH EDITION PAGE.499