Detroit is famous for its automobile industry, making option 3 the correct answer. Detroit, also known as the "Motor City," has a long history and strong presence in the automotive industry. It is home to the headquarters of the "Big Three" automakers – General Motors, Ford, and Chrysler.

Option 1, Textile, is incorrect. While Detroit does have a history of textile manufacturing and a few textile companies, it is not primarily known for this industry.

Option 2, Food processing, is also incorrect. While Detroit does have a diverse food scene and some food processing plants, it is not particularly renowned for this industry.

Option 4, Locomotives, is incorrect. Detroit does not have a significant history or presence in the locomotive industry.

In summary, option 3, Automobiles, is the correct answer as Detroit is famous for its automobile industry and is often referred to as the "Motor City."