The __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ carries low oxygen blood to the lungs and brings high oxygen blood back to the heart.

Pulmonary blood vessel

Explanation:

The pulmonary blood vessel carries low oxygen blood to the lungs and brings high oxygen blood back to the heart.

More specifically, the pulmonary artery carries low-oxygen blood to the lung from the right ventricle of the heart. The blood becomes oxygenated in the lung and the oxygen-rich blood is taken back to the left atrium of the heart by the pulmonary vein.

b. the carbon cycle ensures living things have a source of hydrogen