Darwin learned that there were resemblances between the plants and animals of south america and

increase soil erosion                                             reduce soil erosion

cattle grazing                                                         hydroseeding

deforestation                                                         contour plowing

                                                                                planting vegetation

plant roots basically hold the top soil

together and stop soil erosion because

in such situation top soil is not removed

during flood but cattle grazing causes

soil erosion because cattle consume the

grasses and herbs and top soil is exposed.

same situation occurs because of

deforestation, the trees and plants are cut

down to expose top soil which causes soil

erosion

the answer would be knowledge about cars!