Red blood cells
Red blood cells are the cells which forms the solid part of the blood and floats over the liquid plasma. They consists of a protein called as hemoglobin whose function is to bind the oxygen gas and circulate it to all the parts of the body. Oxygen is the required gas for survival of the living beings as it helps in maintaining the cellular metabolism.
a. red blood cells
Best way to answer this question would first to eliminate all the unnecessary information, such as "which component of the cardiovascular system" because this means the same thing as vascular system and (blood) circulatory system. This consists of the heart and blood vessels. The heart/arteries carry the blood away from the heart and the veins carry it back to the heart. (circulatory)
Now we have, "allows the body to function by supplying the cells with oxygen..."
Now let's review your answers. Plasma. Plasma is the liquid, water-like substance that surrounds the blood cells. Kind of like a fish in water; the fish being the cell and the water being the plasma. So this is not the right answer.
White blood cells or WBC's are your immune system defense. These leukocytes protect and fight against foreign invaders and other infectious diseases within your body. So this is not the correct answer.
Platelets which are referred to as "thrombocytes" are responsible for clotting of the blood. They are disk-shaped cell FRAGMENTS and do not have a nucleus. Notice I pointed out that it is a cell fragment and not a cell. Thus this is not the correct answer either.
Finally, we have Red Blood cells. Also known or abbreviated as RBC's. These cells are produced from within your bone marrow. One function they serve is to remove carbon-dioxide from your body. They carry it to the lungs for you to exhale, thus secreting it from your body. Also within these RBC's is what's known as, "Hemoglobin." This hemoglobin is a protein that carries oxygen. So Red Blood Cells or RBC's would be the correct answer BASED SOLELY ON THE ANSWERS YOU PROVIDED.
If these were not the answers and it was based on the first portion of the question as to which component of the cardiovascular system...your answer would most likely be the heart. It is the component that pushes the blood around the body and the blood contains the oxygen. You will find that the brain and heart are two major roles that allow the body to function the way it does.
The circulatory system is important in meeting the needs of all cells in the body because it offers means of transport by which cells obtain the materials needed to live and function.Superior and inferior vena cava enters the right atrium which is pumped by the tricuspid valve to the right ventricle and to the pulmonary valve to the pulmonary artery then to the lungs from the lungs back thru the pulmonary veins entering the left atrium pumped by the mitral valve to the left ventricle to the aortic valve to the aorta.
red blood cells
Red blood cells supply oxygen and nutrients to the muscles and other parts of the body.