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': 'Parotid duct opens at \nSelect and explain. \nA. 1st PM, B. 1st molar, C. 2nd upper molar, D. 2nd lower molar', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]