This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'National switch day for polio vaccine is \nSelect and explain. \nA. April 25, 2016, B. April 26, 2017, C. April 24, 2025, D. April 23, 2014', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Change over from trivalent to bivalent oral polio vaccine vaccine is National switch day. It was on\xa0April 25, 2016.', 'role': 'assistant'}]