This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': "Toxic megacolon is most commonly associated with- \nSelect and explain. \nA. Ulcerative colitis, B. Crohn's disease, C. Whipple's disease, D. Reiter's disease", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]