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
Commonest Organism Producing acute pyelonephritis 
Select and explain. 
A. Staphylococcus, B. Streptococcus, C. E.coli, D. Salmonella
C: E.coli
Answer: C: E.coli 
Explanation: None