What is the main function of white blood cells?

White blood cells, or leukocytes, play a crucial role in the immune system, primarily defending the body against infections and foreign invaders. They identify and eliminate pathogens such as bacteria, viruses, and other microorganisms that can cause illness. This function is vital for maintaining overall health and preventing disease. Various types of white blood cells, including lymphocytes, neutrophils, and monocytes, each have specialized roles in identifying, targeting, and destroying harmful entities.

The other options represent functions of different cells in the body. For instance, red blood cells are responsible for transporting oxygen to tissues, while the digestive system, aided by various enzymes and cells, facilitates digestion. Regulating body temperature is primarily managed by the hypothalamus and does not pertain to the role of white blood cells. Therefore, option C accurately captures the main function of white blood cells in the context of the immune system.