As blood is pumped by the heart directly into the aorta, the blood travels at 30 . From the aorta, blood flows into the arteries and arterioles and, ultimately, to the capillary beds. As it reaches the capillary beds, the rate of flow is dramatically (one-thousand times) slower than the rate of flow in the aorta. So, the correct option is 'Because of their small size, capillaries contain blood that is moving more quickly than in other parts of the circulatory system'.

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