Which of the following statements is true regarding blood vessels?

The statement that capillaries link arteries and veins is correct because capillaries serve as the tiny vessels that connect the arterial and venous systems within the circulatory system. They facilitate the exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues. This network of capillaries allows oxygenated blood transported through arteries to deliver oxygen to the body's cells and, in return, helps collect carbon dioxide and other metabolic waste products to be carried away through veins.

In contrast to the correct statement, the other options present inaccuracies about blood vessels. For example, it is not true that all vessels carry oxygenated blood, as veins typically carry deoxygenated blood back to the heart. Furthermore, while arteries primarily carry blood away from the heart, the phrasing of that option could be misleading if it doesn't specify that there are exceptions, like pulmonary arteries which carry deoxygenated blood to the lungs. Lastly, veins actually have thinner walls than arteries, which is reflective of the lower pressure within the venous system. Thus, the accurate statement describes the vital role of capillaries in linking the two main types of blood vessels.