Final answer:
Plasma, which is about 55 percent of blood by volume and is mainly composed of water, makes up the largest portion of blood volume. the correct option is a.
Step-by-step explanation:
The element of blood that comprises most of its volume is plasma. Plasma makes up about 55 percent of blood by volume and consists predominantly of water. Along with water, plasma contains dissolved substances like proteins, glucose, ions, hormones, and gases. It serves as the medium for carrying blood cells such as red blood cells (erythrocytes), white blood cells (leukocytes), and platelets throughout the body. Therefore, the correct answer to which element makes up the majority of blood volume is A) plasma.