Vaccines work by exposing the immune system to weakened or inactive forms of a pathogen. The immune system responds by producing antibodies and memory cells. If the person later encounters the actual pathogen, these memory cells quickly mount a defense, often preventing illness entirely or reducing its severity.
It can be inferred from the text that
vaccines directly kill pathogens in the body
the immune system cannot learn to recognize threats
memory cells are destroyed after initial vaccination
the immune system can be trained to recognize and respond to specific threats more effectively
Correct Answer: D
Choice D is the best answer. Vaccines prepare the immune system for future encounters.
- Context clues: Exposure produces "memory cells" that "quickly mount a defense" upon later encounter.
- Meaning: The immune system learns from the vaccine experience.
- Verify: Preventing illness or reducing severity shows improved response.
💡 Strategy: When a process enables better future performance, infer a training or learning mechanism.
Choice A is incorrect because vaccines prepare the immune system—they don't directly kill pathogens. Choice B is incorrect because memory cells show the immune system does learn. Choice C is incorrect because memory cells must persist to respond to later encounters.