Generate an image showing a diverse group of people in business attire working on a large table. They are working on maps and globes, analyzing charts on digital screens. They discuss, write, and calculate data. This represents a national scale trade optimization process. In the background, show some primary industries like farming and mining, transitioning to secondary ones like factories. Then, illustrate advanced technologies such as fast trains, shipping trucks, airplanes, and internet switching centers to depict efficient exchange methods. The scene design should emphasize the ideas of economics, connectivity, and technological advancement.

Which option best analyzes how exchange becomes more efficient at a national scale?(1 point)

a. Quaternary industries develop that benefit existing retail structures in local economies by connecting them to other places around the country

b. Urban centers refocus on primary industries, leading to the development of secondary industries that encourage exchange.

c. Countries enter into treaties that encourage trade, such as the North American Free Trade Agreement.

d. Places within a country specialize based on comparative advantage, meanwhile better technologies enable exchange.

d. Places within a country specialize based on comparative advantage, meanwhile better technologies enable exchange.