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: Dental
[{'content': 'Floor of sinus is closest to the \nSelect and explain. \nA. Roots of first molars, B. Roots of second premolar, C. Roots of first premolar, D. Roots of 2nd molar', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]