Final answer:
Option d) Innate immunity is present without a stimulus and is the correct answer to the student's question. In contrast, vaccination triggers artificially acquired active immunity, which is a part of adaptive immunity.
Step-by-step explanation:
The type of immunity that exists even in the absence of a stimulus is D. innate immunity. Innate immunity includes physical and chemical barriers, immune system cells that attack foreign cells, and proteins that protect the body in general ways. This immunity is naturally existing from birth and does not rely on previous exposure to a pathogen or other foreign substance.
Vaccination triggers A. Artificially acquired active immunity, which is part of adaptive immunity. Adaptive immunity is developed after the body is exposed to an antigen, such as a vaccine, and it creates a long-term memory against that specific pathogen.