the blood vascular system of mammals is known as double vascular system because

Options

A. A group of veins carry oxygenated and other group conducts deoxygenated blood
B. Oxygenated blood runs from heart to different organs by one set of veins while deoxygenated blood runs from heart to lung by another set
C. The two different systems never meet
D. All of the above

Answer

D

Explanation

The pulmonary vein carries the oxygenated blood from the lungs to the heart. The superior and inferior venaecavae carry deoxygenated blood from the upper and lower systematic circulation.
In mammals there are two circulations- systemic (between heart and body) and pulmonary (between heart and lungs).