The correct answer is B) Railroads stimulated economic development.
The most significant effect of the growing railroad system was that Railroads stimulated economic development.
Railroads changed the way people traveled and did business in the United States. After many years of transporting goods and people in horses or wagons, the advent of the United States Railroad system facilitated the movement of people and strengthen trade between the states.
However, the maximum accomplishment of that time was the conclusion of the Transcontinental Railroad on May 10, 1869, that connected the Pacific West with the Eastern Coast of the United States.