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
Most common site of obstruction in chronic dacryocystitis in adults is: 
Select and explain. 
A. At upper end of nasolacrimal duct, B. At lower end of nasolacrimal duct, C. In the lacrimal sac, D. In the common canaliculus
A: At upper end of nasolacrimal duct
Answer: A: At upper end of nasolacrimal duct 
Explanation: Ans. At upper end of nasolacrimal duct