{HEAD ~ The rate} of hardening, or polymerization, of adhesive can be controlled by varying {TAIL ~ the concentration} of catalyst in the catalyst solution 
controlled by varying
{ HEAD ~ The rate } of hardening , or polymerization , of adhesive can be controlled by varying { TAIL ~ the concentration } of catalyst in the catalyst solution
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH