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
Floor of sinus is closest to the 
Select and explain. 
A. Roots of first molars, B. Roots of second premolar, C. Roots of first premolar, D. Roots of 2nd molar
A: Roots of first molars
Answer: A: Roots of first molars 
Explanation: None