Correct Option: B

If the oxygenated blood and deoxygenated blood mixed, then blood would circulate through the body without being fully oxygenated. Also the deoxygenated blood is supposed to take that trip through the lungs to give up the carbon dioxide. The mixing of oxygenated and deoxygenated blood takes place in amphibians and most of the reptiles because thier heart is generally 2 or 3 chambered and do not prevent the mixing of oxygeneted and deoxygeneted blood. Humans have a 4 chambered heart. Our heart follows the process of double circulation.