When you examine fluid that you have drawn from a blood vessel in someone's arm, you find that it is relatively high in carbon dioxide and waste products. Assuming that the fluid comes from a healthy individual, you conclude that the blood vessel from which you have drawn blood could have been .

The given blank can be filled with a venule.

Explanation:

A small blood vessel in the microcirculation, which connects the capillary beds to the veins is known as the venules. Various venules combine to form a vein. The walls of a venule are formed of three layers, that is, the inner endothelium formed of squamous endothelial cells, a middle layer of elastic and muscle tissue, and an external layer formed of fibrous connective tissue.  

The size of a venule ranges from 8 to 100 micrometers in diameter and are produced when capillaries come in close association. A venule refers to a small blood vessel that permits the deoxygenated blood high in carbon dioxide and waste products to return from capillary beds to the bigger blood vessels known as veins.