This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inflammatory Bowel Disease, Subject name: Medicine
[{'content': 'Invariably involved site in ulcerative colitis; \nSelect and explain. \nA. Sigmoid colon, B. Transverse colon, C. Ileum, D. Rectum', 'role': 'user'}, {'content': "Answer: D \nExplanation: Most common site involved in ulcerative colitis is the rectum. Rectum is usually spared in Crohn's disease.", 'role': 'assistant'}]