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
A 7 year old boy living in a low socio-economic background presenting with ocular complaints, was found to have nodules on the bulbar conjunctiva near the limbus. Phlyctenular conjunctivitis is diagnosed. Regarding phlyctenular conjunctivitis TRUE is: 
Select and explain. 
A. Hay fever most common cause, B. Conjunctival edema, C. Redness of eye, D. Pain is rare
D: Pain is rare
Answer: D: Pain is rare 
Explanation: Phlyctenular keratoconjunctivitis is a Type IV delayed hypersensitivity response to microbial proteins, including the proteins of the tubercle bacillus, Staphylococcus species (most common), C albicans, Coccidioides immitis, H aegyptius, and C trachomatis serovars L1, L2, and L3. The conjunctival phlyctenule begins as a small lesion (usually 1-3 mm in diameter) that is hard, red, elevated, and surrounded by a zone of hyperemia. Conjunctival phlyctenules usually produce only irritation and tearing. Ref: Nijm L.M., Garcia-Ferrer F.J., Schwab I.R., Augsburger J.J., Correa Z.M. (2011). Chapter 5. Conjunctiva & Tears. In P. Riordan-Eva, E.T. Cunningham, Jr. (Eds), Vaughan & Asbury's General Ophthalmology, 18e.