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': 'which is true about WIDAL REACTION \nSelect and explain. \nA. Antibody to H antigen appears first and persist, B. Antibody to O antigen appears first and persist, C. Antibodies to H and O antigen appears simultaneously, D. none of the above.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]