This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Pathology, Subject name: Pathology
Which of the following is the earliest manifestation of Crohn disease? 
Select and explain. 
A. Stricture, B. Aphthous ulcer, C. Cobblestone appearance, D. Perforation
B: Aphthous ulcer
Answer: B: Aphthous ulcer 
Explanation: - Among given options, Aphthous ulcer is the earliest manifestation of crohn's disease - Strincture formation; granuloma formation, cobble stone appearance & perforation are relatively late manifestations