The correct answer is option 4: Automobile. Detroit is famously known for being the birthplace of the American automobile industry. It is home to the headquarters and production plants of major automakers such as General Motors, Ford, and Chrysler. The city became a hub for automotive manufacturing in the early 20th century and played a crucial role in the development and growth of the industry. The automobile industry in Detroit brought economic prosperity and contributed to the city`s reputation as the "Motor City." While Detroit was once renowned for its manufacturing capabilities in other industries such as textiles and steel, it is most widely recognized for its association with the automobile industry.