Which of the following is a function of leukocytes?

Leukocytes, commonly known as white blood cells, serve a crucial role in the immune system by fighting infections. They are essential for protecting the body against pathogens such as bacteria, viruses, and other foreign invaders. When the body detects an infection, leukocytes are activated and can proliferate to respond effectively by attacking and neutralizing harmful microorganisms. This function is vital for maintaining health and preventing illness, as leukocytes can also help in the identification and elimination of cancerous cells.

The other choices represent functions associated with different components of blood. For instance, the transport of nutrients is primarily the role of plasma and red blood cells, with red blood cells also being responsible for carrying oxygen throughout the body. Clotting blood is primarily managed by platelets, which play a critical role in the coagulation process to prevent excessive bleeding. Thus, the distinct role of leukocytes in fighting infection highlights their importance in the body's immune response.