This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pancreas, Subject name: Surgery
[{'content': "A 65-year-old woman is admitted with RUQ pain radiating to the right shoulder, accompanied by nausea and vomiting. Examination reveals tenderness in the RUQ and a positive Murphy's sign. A diagnosis of acute cholecystitis is made. What is the most likely finding? \nSelect and explain. \nA. Serum bilirubin levels may be elevated., B. Cholelithiasis is present in 40-60%., C. Bacteria are rarely found at operation., D. An elevated amylase level excludes this diagnosis.", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Stones are found in the gallbladder in over 90% of patients with cholecystitis. Bacteria are cultured in bile in about half the patients undergoing surgery; however, many patients have previously received antibiotics. The gallbladder is usually distended in patients with acute cholecystitis but contracted in chronic cholecystitis.', 'role': 'assistant'}]