The correct answer is - B) by making it possible for natural resources to be transported to different cities and tows.
The expansion and development of the railroads was revolutionary in many aspects, one of which was the availability of natural resources. Before the railroad expansion, the natural resources couldn't be transported to distant location, or only in smaller amounts. While that is not a big problem for the resources like the gold, the ones like the coal and timber are not economically justified nor are of great use if they are transported in small amounts. So once the railroad expansion took place, this all changed, and the natural resources were now possible to be delivered in large amounts over long distances without problems.
