selecting {HEAD ~ content} for and distributing content to users based on {TAIL ~ their association} with the affinity group 
selecting { HEAD ~ content } for and distributing content to users based on { TAIL ~ their association } with the affinity group
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH