The Velocity of Blood Flow Is the Lowest in Capillaries

The velocity of blood flow is the lowest in capillaries because ________.

A) the capillary walls are not thin enough to allow oxygen to exchange with the cells
B) the capillaries have internal valves that slow the flow of blood
C) the diastolic blood pressure is too low to deliver blood to the capillaries at a high flow rate
D) the systemic capillaries are supplied by the left ventricle, which has a lower cardiac output than the right ventricle
E) the total cross-sectional area of the capillaries is greater than the total cross-sectional area of the arteries or any other part of the circulatory system