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
[{'content': 'Azotemia appears when residual GFR is: \nSelect and explain. \nA. 50% -80 % of normal, B. 20-50% of normal, C. 10 -20% of normal, D. < 5% of normal', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Answer is B (20-50% of Normal): Azotemia appears in the stage of Renal Insufficiency when the residual renal function (Residual GFR) is between 20 to 50 percent of normal.', 'role': 'assistant'}]