A. von Thünen's theory of agricultural land use for isolated states states that as distance from a city increases, the type of agriculture changes. Near the city, land is used for high-value crops and intensive cultivation, while further away, land is used for less intensive, lower-value crops. This is based on the concept of decreasing transportation costs as distance from the city increases.
B. One factor related to modern agriculture that invalidates von Thünen's theory is the increased use of mechanization and technology in farming. This has led to a decrease in the need for labor, making it possible to cultivate crops further away from cities without the added cost of transportation.
C. Improved transportation, such as the use of trucks and trains, has made it possible to transport goods over long distances more efficiently and at a lower cost. This has made it possible for farmers to cultivate crops further away from cities, and for consumers to have access to a wider variety of goods, regardless of where they are grown. This invalidates von Thünen's theory because it is no longer necessary to grow crops near the city in order to transport them efficiently.