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
[{'content': 'Most common site of congenital blockage in the nasolacrimal duct is: \nSelect and explain. \nA. At the upper end, B. In the middle, C. At the lower end, D. Whole of the duct', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. At the lower end', 'role': 'assistant'}]