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: Ophthalmology
[{'content': "All are true about Mooren's ulcer except \nSelect and explain. \nA. It is superficial ulcer, B. It spreads circumferentially, C. It is caused by infection, D. Whitish overhanging margins seen", 'role': 'user'}, {'content': "Answer: C \nExplanation: Etiology of Mooren's ulcer is autoimmune not infections.", 'role': 'assistant'}]