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
Average bond strength of second generation dentin bonding agents: 
Select and explain. 
A. 2-5 MPA, B. 12-18 MPA, C. 20-23 MPA, D. 25-30 MPA
A: 2-5 MPA
Answer: A: 2-5 MPA 
Explanation: SECOND GEN - Contains halophosphorus esters of unfilled resins.
Mechanism of bonding Is by ionic bond to calcium by chlorophosphate groups.
Eg: scotchbond, bondlite. 
Disadvantages: 

Again poor bond strength 2-5 MPA. 
Hydrolysis of bond. 
Bonds to smear layer.  

Reference-Sturdevant 6th ed  Pg: 116