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
For GV Black class V cavities, the retainer of choice is 
Select and explain. 
A. No. 212, B. No. 112, C. No. 132, D. No. 221
A: No. 212
Answer: A: No. 212 
Explanation: None