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': 'What is the earliest radiological finding of ulcerative colitis on single contrast barium enema? \nSelect and explain. \nA. Loss of haustrations, B. Fine mucosal granularity, C. Pipe stem colon, D. Collar button ulcer', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The earliest radiological change in UC on single contrast barium enema is fine mucosal granularity. Collar button ulcers and oedematous, thickened haustrations are seen with disease progression. Loss of haustrations is seen with long standing disease.', 'role': 'assistant'}]