The natural resource that became more available to the American public as a result of railroad expansion is coal. Thus the correct answer is C.
What are natural resources?
Elements that are easily accessible financially in the natural world in their undisturbed condition, prior to being modified by human activity are called as natural resources.
The expansion of the railway network resulted in the realization that coal could be used as a form of energy and was also the cheapest or most economical at the time.
Since the majority of mining towns were located in the western, coal made distribution easier throughout the states, and as a result, the US coal industry increased steadily.
Railroads developed to be a significant industry, which promoted the manufacture of other major industries like iron and steel.
Therefore, option C coal is the appropriate answer.
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