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: Radiology
[{'content': 'Earliest radiological feature of ulcerative colitis \nSelect and explain. \nA. Mucosal granularity, B. Pseudo polyps, C. Thumb printing, D. Loss of haustral folds', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Mucosal granularity is earliest sign.', 'role': 'assistant'}]