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
The American dental association (ADA) specification number for non- aqueous elastomeric dental impression material is: 
Select and explain. 
A. 19, B. 20, C. 21, D. 26
A: 19
Answer: A: 19 
Explanation: None