Answer:
 C. herbivore 
Step-by-step explanation:
 A herbivore is an organism that eats plants such as grasses and grains. A carnivore eats other animals to survive so its not a carnivore. An omnivore eats both like people so since omnivores also eat meat, it's not that either. And lastly, A decomposer breaks down organic material such as mushrooms. Therefore, a cow is a herbivore.