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 for Mooren's ulcer except: \nSelect and explain. \nA. Peripheral ulcerative keratitis, B. Advancing edge is undermined, C. Perforation is common, D. Floor of ulcer is quickly vascularised", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Perforation is common', 'role': 'assistant'}]