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': 'Treatment of nasolacrimal duct obstruction: \nSelect and explain. \nA. Syringing, B. Probing, C. DCR, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: A. i.e. Syrignging B. i.e. Probing C. i.e. DCR, D. i.e. Dacryocystectomy', 'role': 'assistant'}]