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
First radiological sign of Crohn's disease in terminal ileum is: 
Select and explain. 
A. Aphthoid ulceration, B. Pseudo sacculation, C. Cobblestone pattern, D. Thickening of bowel wall
A: Aphthoid ulceration
Answer: A: Aphthoid ulceration 
Explanation: Ans. Aphthoid ulceration