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: Surgery
In Caldwell-Luc operation, opening to the sinus is made? 
Select and explain. 
A. At the premolar region, B. At the incisor region, C. At the 1st molar region, D. At the 2nd molar region
A: At the premolar region
Answer: A: At the premolar region 
Explanation: None