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': 'Influenza pandemic is mainly caused by- \nSelect and explain. \nA. Type A, B. Type B, C. Type C, D. All', 'role': 'user'}, {'content': "Answer: A \nExplanation: All known pandemics caused by influenza A strains. Ref:PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition , Page: 153", 'role': 'assistant'}]