Which group of components is common to the circulatory systems of most living animals? A. arteries, veins, capillaries B. vessels, heart, circulating fluid C. aorta, ventricles, atria D. blood, heart, cavities

The circulatory system, composed of the heart, veins, arteries, capillaries, and blood, is a feature common in most vertebrates (animals with a distinct spine). In these animals, blood never leaves the confines of the heart and blood vessels, making theirs a closed circulatory system. In regard to your question, the best answer is B. Some animals have hearts that don’t have atria, while others don’t even have a distinct heart at all.