In what was then the largest environmental enforcement case in US history, companies including industry leaders Caterpillar Inc, Cummins Engine Co, Mack Trucks and Volvo Truck Corp agreed to pay $US83.4 million in fines and reprogram the computers.
In the context of the input sentence, determine the relationship between 'Mack Trucks' and 'Truck'.
Options: product/material produced, original broadcaster, chairperson, headquarters location