The labeling agent is a composition, {HEAD ~ usually a conjugated chemical compound} which has {TAIL ~ two properties} 
has
The labeling agent is a composition , { HEAD ~ usually a conjugated chemical compound } which has { TAIL ~ two properties }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL