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
Which of the following agent is used as a die hardener? 
Select and explain. 
A. Cynoacrylate, B. Nail polish, C. Volatile relief agents, D. Composite Resin
A: Cynoacrylate
Answer: A: Cynoacrylate 
Explanation: None