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': 'Rotavirus infection is diagnosed by the presence of- \nSelect and explain. \nA. Antigen in stool by ELISA, B. Virus in stool, C. Antigen in blood, D. Antibody in stool', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]