This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Pandemics are caused by \nSelect and explain. \nA. Hepatitis B, B. Influenza A, C. Influenza - B, D. Cholera', 'role': 'user'}, {'content': "Answer: B \nExplanation: An epidemic usually affecting a large population of the population, occurring over a wide geographic area such as a section of a nation, the entire nation, a continent or the world eg. influenza pandemics of 1918 and 1957, cholera EI Tor in 1962 and acute haemorrhagic conjunctivitis in 1971 and 1981 Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 101", 'role': 'assistant'}]