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
First dentin bonding agent was: 
Select and explain. 
A. Sevitron cavity seal, B. Cervident, C. Clearfill, D. None
A: Sevitron cavity seal
Answer: A: Sevitron cavity seal 
Explanation: During the 1950s, it was reported that a resin containing glycerophosphoric acid dimethacrylate (GPDM) could bond to a hydrochloric acid–etched dentin surface. Another researcher had used the same monomer chemically activated with sulinic acid and that combination would later be known commercially as Sevitron Cavity Seal (Amalgamated Dental Company, London, England).
Sturdevant Operative Dentistry 7th edition page 142-143