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
Earliest radiological feature of ulcerative colitis 
Select and explain. 
A. Mucosal granularity, B. Pseudo polyps, C. Thumb printing, D. Loss of haustral folds
A: Mucosal granularity
Answer: A: Mucosal granularity 
Explanation: Mucosal granularity is earliest sign.