Which scenario best describes naturally acquired active immunity?

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Naturally acquired active immunity is when the body's own immune system encounters a real pathogen in the environment and activates a targeted adaptive response, creating memory cells for long-term protection. In this scenario the host responds to an actual infection, activating B cells to make antibodies and T cells for cellular immunity, with memory cells that allow a faster, stronger response if re-exposed.

This differs from immunity produced by vaccines (artificial active immunity, since the exposure is via a vaccine, not natural infection), immunity transferred from mother to fetus (natural passive immunity, where antibodies are transferred but the child’s immune system isn’t actively responding), and immunity through administration of antibodies (passive immunity, providing immediate but temporary protection without creating memory).