{HEAD ~ The color formers} and color developers combine upon {TAIL ~ exposure} to an imaging force, such as heat or pressure, to form different colored visible areas on the sheet 
combine upon
{ HEAD ~ The color formers } and color developers combine upon { TAIL ~ exposure } to an imaging force , such as heat or pressure , to form different colored visible areas on the sheet
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH