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