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: Surgery
[{'content': 'The commonest site of obstruction in Gall stone ileus is - \nSelect and explain. \nA. Proximal ileum, B. Distal ileum, C. Ileocecal junction, D. Transverse colon', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Distal ileum", 'role': 'assistant'}]