Final answer:
The cow is the herbivore among the listed options. It primarily eats plants and has a digestive system adapted for processing plant material.
Step-by-step explanation:
The question asks to identify which of the following is a herbivore: 1) cow 2) lion 3) bear 4) grass. A herbivore is an animal that primarily eats plants. Among the options provided, the cow is a herbivore. Cows are known for grazing on grass and other plant materials. In contrast, lions are carnivores that eat meat, bears are generally omnivores that eat both plants and meat, and grass is not an animal but a plant.
Herbivores have evolved digestive systems that are capable of handling fibrous plant material, and they may have specialized mouthparts or teeth for this purpose. Cows are classic examples of herbivores and exhibitors of grazing behavior, as they consume significant amounts of plant material such as grass.