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: Pathology
[{'content': 'What is true about ulcerative colitis \nSelect and explain. \nA. Involves rectum and then whole colon backwards, B. Involves only colon, C. Skip lesions seen, D. Ileum not involved', 'role': 'user'}, {'content': "Answer: A \nExplanation: Classically, ulcerative colitis begins in the rectum, and in continuity extends upwards into the sigmoid colon, descending colon, transverse colon, and sometimes may involve the entire colon. The colonic contents may rarely backflow into the terminal ileum in continuity, causing 'back-wash ileitis' in about 10% of cases. Grossly, the characteristic feature is the continuous involvement of the rectum and colon without any uninvolved skip areas compared to Crohn's disease. TEXTBOOK OF PATHOLOGY 6TH EDITION HARSH MOHAN PAGE NO:567,568 IMAGE REF: GENERAL AND SYSTEMIC PATHOLOGY RAMDAS 2ND EDITION, PAGE 509", 'role': 'assistant'}]