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
Mandibular 1st molar has: 
Select and explain. 
A. 2 roots and 2 canals, B. 2 roots and 3 canals, C. 3 roots and 3 canals, D. 3 roots and 4 canals
B: 2 roots and 3 canals
Answer: B: 2 roots and 3 canals 
Explanation: None