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': 'Von magnus phenomenon is \nSelect and explain. \nA. High hemagglutinin titre, low infectivity, B. High hemagglutinin titre, high infectivity, C. Low hemagglutinin titre, low infectivity, D. Low hemagglutinin titre, High infectivity', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Commonly\xa0hemagglutinin titre\xa0α Infectivity but in Von-Magnus phenomenon - High hemagglutinin titre, Low infectivity due to mutation in virulent gone.', 'role': 'assistant'}]