This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
[{'content': 'A 40 year old male presented to casualty with severe pain in the left upper abdomen radiating to groin. Urine routine shows 6-8 pus cells and 15-20 RBCs. CT scan was taken. What is the diagnosis? \nSelect and explain. \nA. Aoic Aneurysm, B. Acute cholecystitis, C. Left ureteric calculus, D. Acute Colitis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: A non-contrast CT clearly shows a calculus in the left upper ureter', 'role': 'assistant'}]