This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Conjunctiva, Subject name: Ophthalmology
[{'content': 'Pterygyum is usually? \nSelect and explain. \nA. Temporal, B. Nasal, C. Tropical, D. Neoplastic', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pterygium is usually common in tropical countries. Reference: AK Khurana 7th edition page.80,81', 'role': 'assistant'}]