Answer: Katie's experiment most likely represents the interactions between the hydrosphere, geosphere, and biosphere.
Explanation: Oceans are a part of the hydrosphere. Hence, oceans and hydrosphere cannot be separated from each other. The hills and the beach in Katie's experiment represent the geosphere. The toothpicks that she has used to show oats and vegetation are there to represent the biosphere. The existence of these three spheres is always complementary to each other as these spheres are engaged in an eternal interaction with each other.