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
Tooth most frequently requiring RCT is: 
Select and explain. 
A. Mandibular 1st molar, B. Maxillary 1st molar, C. Mandibular 2nd premolar, D. Maxillary 2nd premolar
A: Mandibular 1st molar
Answer: A: Mandibular 1st molar 
Explanation: The most common tooth to be affected is mandibular first molar.
Teeth most frequently requiring RCT is mandibular first molar.