Which of the following statements is true? 1. The largest veins and arteries have the thinnest walls so that oxygen and carbon dioxide can diffuse in and out of those vessels.

2. The farther away the blood vessel is from the heart, the smaller the diameter it has.
3. The farther away the blood vessel is from the heart, the less oxygen the blood in it carries.
4.Because veins carry blood from the feet to the heart, they must have the most smooth muscle in order to pump the blood upward.

The statement that is true is: 2. The farther away the blood vessel is from the heart, the smaller the diameter it has.

The statement that is true is: 2. The farther away the blood vessel is from the heart, the smaller the diameter it has.

This statement is correct because as blood flows away from the heart, it travels through progressively smaller blood vessels, including arterioles and capillaries. These vessels have smaller diameters compared to the larger arteries closer to the heart.