This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'Not true regarding influenza virus is- \nSelect and explain. \nA. All types exhibit antigenic shift, B. Only type A shows antigenic drift, C. Drift is accumulation of point mutations, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The influenza A virus is unique among the viruses because it is frequently subject to antigenic variation, both major and minor. When there is a sudden complete or major change, it is called a shift, and when the antigenic change is gradual over a period of time, it is called a drift . Antigenic shift results from genetic recombination. Antigenic drift involves point mutation. Ref:PARK&;S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition , Page :154', 'role': 'assistant'}]