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': 'A boy is suffering from acute pyelonephritis \nSelect and explain. \nA. WBC casts, B. Leucocyte esterase test, C. Nitrite, D. Bacteria in gram stain', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a. WBC casts', 'role': 'assistant'}]