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
Which of the following is the earliest sign of ulcerative colitis on double-contrast barium enema study - 
Select and explain. 
A. Mucosal granularity, B. Loss of haustrations, C. 'Collar - button' ulcer, D. Lead pipe colon
A: Mucosal granularity
Answer: A: Mucosal granularity 
Explanation: Earliest radiological change of UC on barium enema is blurring of the mucosal lining and a fine granularity when mucosa is seen enface due to edema.
Earliest radiological change of Crohn's disease → Aphthous lesions (Bull's eye or Target lesions).