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
Phlycten is due to – 
Select and explain. 
A. Exogenous allergy, B. Endogeneous allergy, C. Viral keratitis, D. Fungal keratitis
B: Endogeneous allergy
Answer: B: Endogeneous allergy 
Explanation: Phlyctenular conjunctivitis → Endogenous allergy
Vernal keratoconjunctivitis →     Exogenous allergy