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.
What is the relationship between 'Volvo' and 'Truck' in the context of the input sentence.
Options: manufacturer, product/material produced, chief executive officer, headquarters location