The correct option is C Grains
Humans and crows are omnivores while the horse is a herbivore. Herbivores feed on plant-based food while omnivores feed on both plant and animal-based food. The common food item between them is plant-based food items. Hence, animal-based foods like egg, meat, and worms cannot be chosen. This makes grains, a plant-based food, the best choice to feed all.