Because you have to know how is the influence of the steep of the slope in the time that a ball reaches the bottom. The steep of the slope is the variable that you would have to change in an experiment.
Deer depend on plants to survive because they are herbivores. Herbivores are animals that only eats plants and fruits in order to survive. Deer's meal includes grass and evergreen plants. If grass is unavailable, they eat whatever food like fallen leaves, twigs, bushes and other woody plants.
