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
Example of DBA used as amalgam bonding agent: 
Select and explain. 
A. 2-META, B. 4-META, C. 2-HEMA, D. 4-HEMA
B: 4-META
Answer: B: 4-META 
Explanation: 4 META is applied into the cavity first then amalgam is condensed over it. And finally curing is done.