Which option best analyzes how exchange becomes more efficient at a national scale? ( 1 point )
A.) Countries enter into treaties that encourage trade, such as the North American Free Trade Agreement.
B.) Urban centers refocus on primary industries, leading to the development of secondary industries.
C.) Quaternary industries develop that benefit existing retail structures in local economies by connecting them to other places around the country.
D.) Places within a country specialize based on comparative advantage, meanwhile better technologies enable exchange.