What impact did developments in the steel industry during the 19th century have on the United States?

They made steel stronger and more flexible, allowing for the development of aircraft for the military.
They made the consumption of oil more important, resulting in a growing dependence on foreign energy sources.
They made the production of the steel rails cheaper, helping to spread railroad networks throughout the nation.
They made it possible to manufacture inexpensive cars, leading to the construction of interstate highways.

Question

What impact did developments in the steel industry during the 19th century have on the United States?

 They made steel stronger and more flexible, allowing for the development of aircraft for the military.
 They made the consumption of oil more important, resulting in a growing dependence on foreign energy sources.
 They made the production of the steel rails cheaper, helping to spread railroad networks throughout the nation.
 They made it possible to manufacture inexpensive cars, leading to the construction of interstate highways.