Final answer:
Properdin can act as an opsonin for some microbes, including Neisseria gonorrhoeae.
Step-by-step explanation:
The correct answer is a) Opsonin. Properdin, a protein in the complement system, can act as an opsonin for some microbes including Neisseria gonorrhoeae. Opsonization is the process of coating a pathogen with a substance (opsonin) that enhances phagocytosis by immune cells. In this case, properdin aids in the recognition, engulfment, and destruction of Neisseria gonorrhoeae by phagocytic cells such as macrophages and neutrophils.