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
Commonest cause of bronchiolitis: 
Select and explain. 
A. RSV, B. Entero virus, C. Pneumococcus, D. Hemophilus
A: RSV
Answer: A: RSV 
Explanation: Ans: a