16. (08.05 mc) which of the following changes in modern agriculture challenges the validity of von thünen's theory? (3 points) i. increased consumer demand for organic food ii. decreased transportation time from farm to market iii. global demand for certain crops iv. increased mechanization of agriculture has increased crop yields i and ii i and iii i and iv ii and iii ii and iv

The answer is II and IV. Von Thunen's Theory 's proncipal variable is distance. If the crop field is close to the consumption area (a city), the cost of that land will be expensive. If it is far away, the cost of the land will reduce but the transportaions ones will increase. With the improvement of transportation the distance won't be such a determinant factor, those costs reduce considerably.

With the improvement of crop yields, wich Von THunen did not had in consideration, a single crop can provide a lot of food making the cost of the land reduce its importance.

on april 6, 1917, the u.s. joined its allies--britain, france, and russia--to fight in world war i. under the command of major general john j. pershing, more than 2 million u.s. soldiers fought on battlefields in france.