Which Statement About the Human Heart Is True

Which statement about the human heart is true?

A) The walls of the right ventricle are thicker than the walls of the left ventricle.
B) Blood flowing through atrioventricular valves is always deoxygenated blood.
C) The second heart sound is due to the closing of the aortic valve.
D) Blood returns to the heart from the lungs in the vena cava.
E) During systole, the aortic valve is open and the pulmonary valve is closed.