This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nose and PNS, Subject name: ENT
Chronic dacrocystitis is due to? 
Select and explain. 
A. Obstruction in naso lacrimal duct, B. Narrow bony canal, C. Foreign body, D. All of above
D: All of above
Answer: D: All of above 
Explanation: ANSWER: (D) All of aboveREF: Khurana 4th ed p. 370Etiology of chronic dacryocystitis is due to obstruction and stasis AETIOLOGY:Nasolacrimal obstructionNarrow" bony canalExcessive folds in nasolacrimal ductForeign bodyExcessive lacrimationMild grade inflammation