{TAIL ~ Variability} in chemical sensitivity from sensor to sensor is provided by qualitatively or quantitatively varying the composition of {HEAD ~ the conductive and nonconductive regions} 
{ TAIL ~ Variability } in chemical sensitivity from sensor to sensor is provided by qualitatively or quantitatively varying the composition of { HEAD ~ the conductive and nonconductive regions }
TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD