Answer: C. The price of cars increased as demand increased.
Ford's assembly line was revolutionary not only for Ford or for the automobile industry. It affected every industry in the United States. Ford was inspired by slaughterhouses and grain warehouses that used a conveyor belt system. However, his great addition was interchangeable parts. This meant that every car used the exact same parts, so that they could be assembled in an organized and fast way. This decreased the price of the Model T from $850 ($21,000 in today's currency) to $260 ($3,500 today), which increased demand enormously.