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
[{'content': 'Which of the following is the earliest manifestation of Crohn disease? \nSelect and explain. \nA. Stricture, B. Aphthous ulcer, C. Cobblestone appearance, D. Perforation', 'role': 'user'}, {'content': "Answer: B \nExplanation: - 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", 'role': 'assistant'}]