Which can be used to characterize blood flow in the human body?
a: there is a unidirectional blood flow.
b: arteries always carry oxygenated blood.
c: veins always carry deoxygenated blood.
d: arteries carry blood away from the heart.
e: veins carry blood toward the heart.

a: There is a unidirectional blood flow.

d: Arteries carry blood away from the heart.

e: Veins carry blood toward the heart.

Explanation:

The human circulatory system includes three main types of blood vessels: arteries, veins, and capillaries. Arteries are the blood vessels that carry the oxygenated blood from the heart to various body tissues. Veins are the blood vessels that pick the deoxygenated blood from body tissues and deliver to the heart. Vena cava is the largest vein that reaches the right atrium of the heart and delivers the deoxygenated blood.

The blood from the right atrium is carried to the right ventricle and finally lungs via the pulmonary artery for oxygenated. The oxygenated blood from the lungs is carried to the left atrium of the heart by a pulmonary vein. The oxygenated blood from the left atrium is carried to the left ventricle and finally to the body tissues by branches of the aorta. This unidirectional blood circulation of the human body ensures efficient delivery of oxygenated blood to body tissues.