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 shift - \nSelect and explain. \nA. Occurs every 2-3 years, B. Gradual change over time, C. Results from genetic recombination, D. Occurs in all influenza viruses', 'role': 'user'}, {'content': "Answer: C \nExplanation: Antigenic shift is an abrupt, drastic, discontinuous variation in the antigenic structure resulting in a novel virus strain unrelated antigenically to predecessor strain. REF: Anantha Narayan AND PANIKER'S TEXTBOOK OF MICROBIOLOGY 9TH EDITION PAGE NO:499", 'role': 'assistant'}]