What does naturally acquired active immunity mean?

Naturally acquired active immunity refers to the type of immunity that develops in an individual after they are exposed to a pathogen through natural infection. This means that when a person contracts a disease, their immune system responds by producing antibodies and memory cells specific to that pathogen. This natural process leads to long-lasting immunity because the body has a "memory" of the infection, allowing it to respond more effectively if exposed to the same pathogen in the future.

The other options represent different forms of immunity. Immunity gained from vaccines is an example of artificially acquired active immunity, where exposure to a harmless version of a pathogen helps the immune system develop a response. Immunity transferred across the placenta and immunity from breast milk are both examples of passive immunity, where antibodies are supplied rather than produced by the individual's own immune system. Therefore, these options do not capture the essence of naturally acquired active immunity, which is specifically about the body’s own response to an infectious agent.