The blood that flows from lungs to heart is bright red, becuase
(a) it is made red by oxygen
(b) it is made red by carbon dioxide
(c) it is made red by gastric juices
(d) the lungs add a pigment(dye) to blood as it flows through them

Correct Answer: (a) it is made red by oxygen

Explanation:

The pulmonary vein brings oxygenated or clean blood from the lungs into the heart, thus it is made red by the presence of oxygen-carrying hemoglobin.