Answer: D. The refrigerator car
A refrigerator car is more like a mobile refrigerator built to transport perishable goods at cool temperatures through long distances. Just after the American civil war, a major railway centre was established in Chicago, Illinois. To get the animals to the market, vast herds are driven distances of about 1,200 miles even with the risk of food spoilage. After several attempts of transporting perishable items without spoilage, the 1880s paved the way for the refrigerator car; a complete revolution in the meat industry.