The correct answer is - they make their own food.
Nutritionally animals are categorized as heterotrophs. Heterotrophs may be saprophytes rely on dead and decaying materials for food or may be parasites, take food from other living organisms or may be having holozoic mode of nutrition. Heterotrophs cannot synthesize organic compounds such as carbohydrate from inorganic raw materials such as carbon dioxide and water. Therefore, they depend on other organisms for food to get energy. Autotrophs such as green plants can synthesize their own food from inorganic raw materials such as carbon dioxide and water.