Which generation of bonding system combines the primer and bonding agent into a single step?
FIFTH GENERATION  

To decrease the number of steps PRIME AND BOND WERE COMBINED. 
ETCH +   (PRIME+BOND). 
Called self priming adhesive.  
Bond strength 17-24 MPA. 
Less number of steps less post operative sensitivity. 

Eg: Prime and bond NT, Adper single bond, Opti bond solo.
Reference- Sturdevant 6th ed
Fourth
Fifth
Sixth
Seventh