The chain of infection is the basis of disease transmission.

• A. Exit
• B. Reservoir
• C. Basis Of Disease Transmission
• D. Host

Answer: (C)

Understanding how infections spread depends on the chain of infection as the framework for disease transmission. This idea is the best answer because it names the overall structure that connects the infectious agent, the reservoir where it lives, the exit route it uses, the means of transmission, the portal of entry, and the host’s susceptibility. Recognizing this chain helps you see where interruptions can stop spread—remove the reservoir, block exit, disrupt transmission, shield the entry point, or reduce host susceptibility. The other terms are parts of the chain—specific links like where the pathogen resides, how it leaves, or who is susceptible—rather than the overarching framework that explains transmission.