What are the three main components of whole blood?

The three main components of whole blood are plasma, leukocytes, and erythrocytes. Plasma is the liquid portion of blood, comprising about 55% of its volume. It contains water, electrolytes, nutrients, hormones, and waste products. Leukocytes, or white blood cells, play a crucial role in the immune system by defending the body against infection. Erythrocytes, or red blood cells, are responsible for transporting oxygen from the lungs to the body's tissues and returning carbon dioxide from the tissues back to the lungs.

This choice accurately reflects the composition of whole blood, specifically focusing on the cellular (leukocytes and erythrocytes) and liquid (plasma) components that are essential for its functioning. Each element is vital for different physiological processes, such as oxygen transport, immune response, and maintaining fluid balance in the circulatory system.