What involves the injection of live, killed, or attenuated microorganisms?

The injection of live, killed, or attenuated microorganisms refers to a method of stimulating the immune system to produce an immune response, which is characteristic of active artificial immunity. This form of immunity is intentionally provided through vaccination, where the immune system recognizes the antigens from the microorganism and develops a tailored response, including the production of antibodies and memory cells.

When an individual receives a vaccine, their body is exposed to a form of the pathogen (whether live but weakened, killed, or inactivated) that is similar enough to trigger the immune response without causing the actual disease. As a result, if the person is later exposed to the real pathogen, their immune system can quickly recognize and combat it.

Other options refer to different mechanisms of immunity. Passive immunity involves the transfer of pre-formed antibodies from one individual to another, making it immediate but temporary. Cell-mediated immunity is a type of immune response that does not primarily involve antibodies but instead relies on the activation of certain immune cells. Natural immunity occurs through direct exposure to pathogens rather than through vaccination or artificial means. Thus, the correct choice distinctly represents the process of generating an immune response through immunization.