This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Medicine
[{'content': 'Most common site of Gallstone ileus: \nSelect and explain. \nA. Caecum, B. 2nd pa of duodenum, C. Terminal ileum, D. Stomach', 'role': 'user'}, {'content': "Answer: C \nExplanation: Gallstone ileus is an unusual complication of chronic cholecystitis due to impaction of gallstone in ileum after passing through a biliary-enteric fistula. Impacted gallstone usually in the terminal ileum at ileocecal valve Rigler's Triad: Pneumobilia Small bowel obstruction Gallstone at terminal ileum", 'role': 'assistant'}]