This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head and neck, Subject name: Anatomy
[{'content': 'Valve of Hasner \nSelect and explain. \nA. Opening of nasolacrimal duct, B. Sphenoidal sinus opening, C. Frontal sinus opening, D. Ethmoidal sinus opening', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref BDC volume3,6th edition pg 76Nasolacrimal duct begins at the lower end of the lacrimal sac, runs downwards, backward and laterally and opens into the inferior meatus of the nose.A fold of mucous membrane called hasners valve forms an imperfect valve at the lower end of the duct.', 'role': 'assistant'}]