This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
First radiologic sign of Crohn's disease in the terminal ileum is 
Select and explain. 
A. Aphthoid ulceration, B. Pseudosacculation, C. Cobble stone pattern, D. Thickening of bowel wall
A: Aphthoid ulceration
Answer: A: Aphthoid ulceration 
Explanation: .