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
Percentage of distal root with two root canals in mandibular molar 
Select and explain. 
A. 10%, B. 30%, C. 60%, D. 1%
B: 30%
Answer: B: 30% 
Explanation: None