The "chain of infection," i. e., the transmission of infectious agents in healthcare settings requires a

Explanation:

Chain of infection is the term that represents a set of related elements (source of infection, route of elimination, route of transmission, gateway) that demonstrates the process of spreading microorganisms that can cause disease in humans and other animals. . The existence of a chain of infection in healthcare settings requires the existence of a source or reservoir of infectious agents, the existence of a susceptible host with an infectious agent receptive entry portal, and the existence of a mode of transmission to the infectious agent.

d, i believe because of it's activity level