The illustration below shows simplified models of two different circulatory systems.

Diagram at left shows a single loop of blood vessels, including a heart with 1 ventricle and 1 atrium and two capillary beds. At right, a heart with 2 ventricles and 2 atria, and a double loop of blood vessels to two capillary beds.

In both models, which is one way that the real circulatory system is more complex than the model shows?

A. The heart has several additional chambers for receiving and pumping blood.
B. Arteries and veins divide and branch many times to serve all of the body capillaries.
C. A capillary bed interfaces with the digestive system, where gas exchange occurs.
D. Twenty wide arteries extend directly from the heart, each carrying blood to a separate capillary bed.