The answer is A. Transportation costs decreased due to the invention of the railroad, not increased.
The invention of the railroad allowed for faster and more efficient transportation of goods and people, which reduced transportation costs. Prior to the railroad, transportation was slower and more expensive, often relying on animal power or waterways. The railroad made it possible to transport goods and people more quickly and at a lower cost, which helped to fuel economic growth and expansion. The reduction in transportation costs also made it possible to transport agricultural products longer distances, which helped to open up new markets and increase demand for agricultural goods.