Final answer:
The major mechanisms of indirect colonization resistance include enhancement of the epithelial barrier, activation of host immune responses, and competition for space.
Step-by-step explanation:
The subject of this question is Biology. The question is asking about the 3 major mechanisms of indirect colonization resistance. The correct answer is B) Enhancement of the epithelial barrier, activation of the host immune responses, competition for space.
Pathogens can enter the body through various routes and overcome physical and chemical barriers. One of the ways the body defends against pathogens is by enhancing the epithelial barrier, which prevents their entry. Additionally, the host immune responses are activated to fight against the pathogens. Finally, competition for space occurs between the commensal organisms and the pathogens in the body, limiting the growth and colonization of the pathogens.