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': 'All are true about Antigen drift except - \nSelect and explain. \nA. It causes pandemic, B. Occurs due to mutation, C. Occurs frequently, D. Minor antigenic changes', 'role': 'user'}, {'content': "Answer: A \nExplanation: Antigenic drift the gradual sequential change in antigenic structure occuring regularly at frequent intervals. Antigenic drift is due to mutation and selection .It accounts for the periodic epidemics of influenza. REF:ANANTHANARAYAN AND PANIKER'S TEXTBOOK OF MICROBIOLOGY 9TH EDITION PAGE NO-499", 'role': 'assistant'}]