B. The economy crashed because the railroads failed.
Explanation:
Why the railroads were so important-
The railroad industry was the largest employer outside agriculture in the US and involved large amounts of money and risk.
A large infusion of cash from speculators caused spectacular growth in the industry and in teh construction of docks, factories, and ancillary facilities.
The amount of heat radiated from the atmosphere to the surface (sometimes called “back radiation”) is equivalent to 100 percent of the incoming solar energy