This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of the Respiratory Tract, Subject name: Pediatrics
Most common cause of lower respiratory tract infection in 3 year old child is - 
Select and explain. 
A. Klebsella, B. H-influenza, C. Streptococcal pneumonia, D. Staphe aureus
C: Streptococcal pneumonia
Answer: C: Streptococcal pneumonia 
Explanation: Ans. is 'c' i.e., Streptococcal pneumonia Etiology of pneumonia Viral - RSV, Influenza, parainfluenza, adenovirus Responsible about 40% of casesBacteria - Seen in 2/3 of pheumoniaFirst 2 month -o Klebsellao Staphe aureus3 month - 3 year -o S. Pneumoniaeo H. Influenzao Staph aureusAfter 3 year -o 5. Pneumoniao Ataph aureus