The _________ prevent(s) the mixing of oxygenated and deoxygenated blood in the heart.
The heart contains two upper chambers called atria and two lower chambers called ventricles. The left and right sides of the heart are separated by the septum. It prevents mixing the blood. Valves prevent the backflow of blood and separate the atria from the ventricle and the ventricle from the pulmonary artery or aorta.
Therefore, the correct option is D. septum