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: Social & Preventive Medicine
[{'content': 'Mutation is seen in \nSelect and explain. \nA. Poliovirus, B. Influenza virus, C. Mumps virus, D. Measles virus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: A unique feature of the influenza virus is its ability to undergo angenic variaons.\nAngenic variability is highest in influenza virus Type A and less in Type B, while it has not been demonstrated in type C.\nSurface angens hemagglunin and neurominidase, undergo independent angenic variaons which may be of Two types.\n\n1. Angenic dri\n\nAngenic change is gradual over a period of me\nThe new angens, though different from the previous angens, are yet related to them,\nAngenic dri involves point mutaon in the gene owing to selecon pressure by immunity in the host populaon.\nAngenic dri accounts for the periodic epidemics of influenza.\nOccurs every 2-3 years in case of Influenza A and every 4-7 years in case of Influenza-B 2.\n\n2. Angenic shi\n\nAn abrupt, drasc, disconnuous variaon in the angenic structure,\nResult from genec recombinaon of human with animal or avian virus,\nAccounts for the major epidemics or pandemics,\nOccurs every 10-15 years,\nOccurs in influenza ‘A’ only', 'role': 'assistant'}]