The correct answer to this question is false. While it is not the endocardium, "D" represents the aortic semilunar valve. This valve is in the human heart. It is between the aorta and left ventricle. There are three cusps, also known as leaflets, that the aortic valve has. A minority of hearts only have two leaflets.
The aortic semilunar valves has many functions. It helps maintain high pressures in the system circulation, while reducing pressure in the ventricle. This helps blood flow from the lungs fill the ventricle. The aortic semilunar valve also sends blood to the body itself and the heart muscle.