Final answer:
The correct answer is C. complement. The complement system of blood proteins acts to lyse foreign cells and viruses, complementing the antibody response of the immune system.
Step-by-step explanation:
The complement system of blood proteins acts to lyse foreign cells and viruses. This system is made up of approximately 20 soluble proteins that enhance phagocytosis, bore holes in pathogens, and recruit lymphocytes.
The complement proteins function in a cascading fashion to mark and destroy pathogens, complementing the antibody response of the adaptive immune system.