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
At the age of nine years, the mandibular permanent first molar has its distal contact with which of the following teeth? 
Select and explain. 
A. First premolar, B. Second premolar, C. Deciduous 2nd molar, D. None
D: None
Answer: D: None 
Explanation: None