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: Medicine
The MOST COMMON causative organism for community acquired pneumonia is: 
Select and explain. 
A. Streptococcus pneumoniae, B. Haemophilus influenzae, C. Mycoplasma pneumoniae, D. Chlamydia pneumoniae
A: Streptococcus pneumoniae
Answer: A: Streptococcus pneumoniae 
Explanation: Although Streptococcus pneumoniae is most common pathogen causing community aquoired pneumonia. Data suggest that a virus may be responsible for up to 18% of cases of CAP that require admission to the hospital. Ref: Harrison, E-18,P-2131.