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
4 months old infant had respiratory distress.It was diagnosed as bronchiolitis. most common cause of this is 
Select and explain. 
A. Measles, B. Respiratory syncytial virus, C. Influenza, D. Para Influenza virus
B: Respiratory syncytial virus
Answer: B: Respiratory syncytial virus 
Explanation: RSV is the m/c cause of lower respiratory tract infection below 1 year.