Final answer:
The primary defense against extracellular infectious agents includes neutralization, opsonization, and complement activation, all of which work in concert to protect the body; hence the correct answer is D. All of the above.
Step-by-step explanation:
The primary defense against extracellular infectious agents includes multiple strategies such as neutralization, opsonization, and complement activation. Neutralization occurs when antibodies coat extracellular pathogens and block key sites, preventing them from infecting host cells. Opsonization involves the coating of a pathogen with molecules to assist phagocyte binding and facilitate phagocytosis. Complement activation is triggered when antibodies attached to the surface of a pathogen cell activate the complement system, which can destroy the pathogen.
Therefore, the correct answer to the question is D. All of the above as these mechanisms work together to provide a robust defense against infectious agents.