the initial development of the steel industry was most significantly aided by the?

Question

1 - development of city skyscrapers
2- emergence of the petroleum industry
3 - invention of Bessemer and open-hearth processes
4- rapid expansion of the railroads
5 - significant increase in defense spending

Answer 1

3-The Bessemer process made it possible to produce steel of higher purity for a much lower cost. Thse rest of the answers relate to the demand for steel after it was being mass produced by the Bessemer process, except for answer #2, which doesn't make sense because steel furnaces were coal fired for a long time before oil was readily available.