Answer:
d. naturally acquired active immunity.
Step-by-step explanation:
Naturally acquired active immunity refers to the immune response that occurs when a person's immune system is exposed to an antigen through natural means, such as infection or exposure to pathogens in the environment. In this process, the immune system recognizes the antigen, mounts an immune response, and generates specific immune memory cells to provide long-term protection against future encounters with the same antigen. This type of immunity is acquired actively by the individual's immune system actively responding to the antigen.