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': 'The most common early sign of kidney disease is: \nSelect and explain. \nA. Sodium retention, B. Elevated BUN level, C. Development of metabolic acidosis, D. Inability to dilute or concentrate urine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Increased BUN is usually an early indicator of decreased renal function.', 'role': 'assistant'}]