I don't understand the heart! Someone please help me!?

D, c, b, true are correct. The animal and human heart is divided into four chambers. The lower two are called ventricles and the upper two are called atria. Arteries take the blood away from the heart and it's full of oxygen. The biggest artery is the aorta. Cappilaries connect veins to arteries. And veins carry the blood back to the heart. In the veins the blood has little to no oxygen.