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
Pterygyum is usually? 
Select and explain. 
A. Temporal, B. Nasal, C. Tropical, D. Neoplastic
C: Tropical
Answer: C: Tropical 
Explanation: Pterygium is usually common in tropical countries. Reference: AK Khurana 7th edition page.80,81