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
Most common organism causing UI in adult? 
Select and explain. 
A. H influenza, B. Stap aureus, C. Strepto pneumonia, D. Streptococcus pyogenes
D: Streptococcus pyogenes
Answer: D: Streptococcus pyogenes 
Explanation: Ans. is 'd' i.e., Streptococcus pyogenes Most common cause of upper respiratory tract infection is viral infection. Rhinovirus is the most common cause. Among the bacteria, group A beta-hemolytic streptococci (streptococcus pyogenes) is the most common cause. And most common type of infection is pharyngitis.