Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: A single-replacement reaction is one in which an element replaces another element in a compound. An element is in either the solid, liquid, or gas state and is not an ion. The example below shows the reaction of solid magnesium metal with aqueous silver nitrate to form aqueous magnesium nitrate and silver metal. Answer: single-replacement reaction
[A]: In this type of reaction, an element replaces another element in a compound, and the element is in any state of matter but is not an ion?

[Q]: Passage: Virtually all animals have internal digestion of food. Animals consume other organisms and may use special tissues and organs to digest them. (Other heterotrophs, such as fungi, absorb nutrients directly from the environment. ). Answer: internal
[A]: What sort of digestion do animals engage in?

[Q]: Passage: As pictured below ( Figure below ), some grazing animals, especially sheep and goats, eat grass right down to the roots. They may even pull the grass entirely out of the ground. Grazing animals can kill the grass. They may thin it out so much that it offers little protection to the soil. If animals are kept in the same place too long, the soil may become completely bare. The bare soil is easily eroded by wind and water. Answer: erosion
[A]:
By pulling out grass by its roots and over-grazing, livestock contribute to what negative process?