Blood being pumped by the heart is circulated in two circuits. One circuit carries blood with high levels of to the lungs, and the other circuit carries blood with high levels of to the body.

Carbon dioxide, Oxygen

Explanation:

The circulatory system of our body works following two pathways -

In pulmonary pathway the deoxygenated blood is carried to the lungs while in the second pathway, known as systemic pathway, the oxygenated blood is carried to the various parts and organs of our body. Thus the completed sentence in the question will be -

Blood being pumped by the heart is circulated in two circuits. One circuit carries blood with high levels of carbon dioxide to the lungs, and the other circuit carries blood with high levels of oxygen to the body.

The preferable words for the given fill in the blanks will be -  

Carbon Dioxide

Oxygen

Explanation:

Blood is pumped by the heart is circulated in two circuits. One circuit carries blood with high levels of Carbon Dioxide to the lungs, and the other circuit carries blood with high levels of oxygen to the body.

human-caused climate hope this