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: Surgery
Ulcerative colitis stas from: 
Select and explain. 
A. Rectum, B. Sigmoid colon, C. Ascending colon, D. Any pa
A: Rectum
Answer: A: Rectum 
Explanation: Rectal involvement (proctitis) is the hallmark of the disease, and the diagnosis should be seriously questioned if the rectal mucosa is not affected.