Final answer:
During systole, the heart's contraction increases aortic pressure due to the increased volume of blood being pumped into it, causing the walls of the aorta to stretch.
Step-by-step explanation:
The increased aortic pressure that occurs during systole reflects an increased volume of blood in the aorta (Option D). During systole, the heart contracts, pushing blood into the aorta and causing the pressure to rise. This rise in pressure is due to the additional volume of blood entering the aorta which causes the walls to stretch to accommodate the increased volume. There's no decreased resistance of the vasculature or decreased volume of blood within the aorta during systole, and while increased resistance could also cause an increase in aortic pressure, in the context of systole, the predominant factor is indeed the increased volume of blood being pumped out of the heart. The stiffness of the aorta contributes to how well it can accommodate this change in volume, with less compliant (more stiff) arteries contributing to higher systolic pressures.