This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small & Large Intestine, Subject name: Surgery
[{'content': 'Ulcerative colitis most commonly involves: \nSelect and explain. \nA. Rectum, B. Anus, C. Ascending colon, D. Ileum', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. (a) RectumRef: Sabiston 20th edition, Page 1339* Most common site of ulcerative colitis: Rectum* Most common site of Crohn's disease: Terminal ileum", 'role': 'assistant'}]