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
Terminal mandibular molar anchor teeth requiring preparations involving the distal surface; retainer used is 
Select and explain. 
A. W27, B. W56, C. W7, D. W8
A: W27
Answer: A: W27 
Explanation: None