The expansion of the railroad directly led to economic growth in the us because
a. railroads increased competition between different industries.
b. railroads allowed company owners to travel all over the country.
c. railroads made resources and products easier to transport.
d. railroads led to increased prices of newly available products and resources.

The correct answer is:

C. railroads made resources and products easier to transport.

Explanation:

With the growth of railroads in the United States by the late 1800s, industrialization also grew in many cities because it gave access to more products and resources to produce those products, and people began trading and consuming those products faster, the commerce was stimulated because there was bigger demand and supply and this led to economic growth. Rural towns transformed into urban cities, and railroads were a key factor in this transformation.