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: Anatomy
[{'content': "Which valve is present at opening of nasolacrimal duct? \nSelect and explain. \nA. Hasner's valve, B. Heister valve, C. Spiral valve, D. None", 'role': 'user'}, {'content': "Answer: A \nExplanation: Nasolacrimal duct opens into inferior meatus and is closed by a mucosal flap called Hasner's valve.Heister valve (spiral valve) is present in cyctic duct.", 'role': 'assistant'}]