A student made a model of a river in a sandbox. A pile of sand represents soil and bits of rock in the riverbed. Water pouring from a hose represents river water as it flows downhill Which two characteristics are limitations of the student's model? A. The model soil is nothing like the soil found in a real riverbed. B. The model is much smaller than a real river. C. The model river water flows downhill instead of uphill like real river water does. D. The model is missing plants, fish, and other details found in a real river.