This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Pediatrics
[{'content': 'Commonest cause of bronchiolitis: \nSelect and explain. \nA. RSV, B. Entero virus, C. Pneumococcus, D. Hemophilus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: a', 'role': 'assistant'}]