This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Medicine
[{'content': 'Most common site of ulcerative colitis is ? \nSelect and explain. \nA. Rectum, B. Caecum, C. Small intestine, D. Appendix', 'role': 'user'}, {'content': 'Answer: A \nExplanation: <p>Davidson&;s principles and practice of medicine 22nd edition. *ulcerative colitis invariably involves the rectum and spread proximally in continues manner it involves the entire colon in some cases.</p>', 'role': 'assistant'}]