In {HEAD ~ the described embodiment}, {TAIL ~ the ad selection process} is “decoupled” from the ad content delivery process 
In { HEAD ~ the described embodiment } , { TAIL ~ the ad selection process } is “ decoupled ” from the ad content delivery process
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH