A human red blood cell in an artery of the left arm is on its way to deliver oxygen to a cell in the thumb. To travel from the artery to the thumb and then back to the left ventricle, this red blood cell must pass through .
a. one capillary bedsb. two capillary bedsc. three capillary bedsd. four capillary bedse. five capillary beds

(b). two capillary beds.

Explanation:

A human has a complete circulatory system that plays an important role in the circulation of the blood in the body of the human. Generally, there are two vessels that are responsible to transport the oxygenated blood and deoxygenated blood in the body. Generally, the artery carries oxygenated blood except for the pulmonary artery and the other is the vein that transports the deoxygenated blood except for the pulmonary vein. Capillaries are the microscopic vessel that is originated from the artery and connects the venules. When they are present in the form of a network  is generally known as capillary beds and plays an important role in the exchange of nutrients, gases and other materials between the tissues cells and the blood. They are categorized as two capillaries bed, three capillaries bed and some other on the basis of the capillary in a  network. Two capillary beds play an important role in the delivery of blood from the heart to the thumb and from thumb to the left ventricles.