Which of the causes of the Second Industrial Revolution had the biggest impact on the Revolution ?

Railroads allowed cheap transportation of materials and products, which in turn led to cheap rails to build more roads. Railroads also benefited from cheap coal for their steam locomotives. This synergy led to the laying of 75,000 miles of track in the U.S. in the 1880s, the largest amount anywhere in world history.

Explanation:

4 copper and gold, the california gold rush is why im pretty sure.

answer; i believe its (jade); good luck