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 cause of pyelonephritis in pregnancy: 
Select and explain. 
A. Pseudomonas, B. E. coli, C. Proteus, D. Klebsiella
B: E. coli
Answer: B: E. coli 
Explanation: Ans. is. 'b' i. e., E. coli