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: Pathology
[{'content': 'An important factor for chronic pyelonerphritis is - \nSelect and explain. \nA. Obstruction, B. Vesico-ureteral reflux, C. Pelvi-ureteric junction obstruction, D. Catheter induced', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]