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 Rosenmuller is located at \nSelect and explain. \nA. Cystic duct, B. Opening of nasolacrimal duct, C. Junction of lacrimal sac and canaliculus, D. Ampulla of vater', 'role': 'user'}, {'content': 'Answer: C \nExplanation: A fold of mucous membrane found at the junction between the common canaliculus and the lacrimal sac. It is not strictly a valve because fluids can be blown back to emerge at the puncta. It is not always fully developed. ref -medscape.com', 'role': 'assistant'}]