Which of the following is considered a type of active immunity?

Active immunity is a form of immunity that occurs when an individual's immune system is exposed to a pathogen and actively produces an immune response. This can happen through natural exposure to pathogens, which leads the body to stimulate the production of specific antibodies and memory cells that provide long-term protection against future infections.

Natural exposure to pathogens involves being infected with a disease-causing organism, which prompts the immune system to respond and build immunity to that specific pathogen. This type of immunity can provide long-term benefits, as the immune system retains a memory of the pathogen, allowing for a more rapid and effective response if the individual is exposed to the same pathogen again in the future.

Other options like the injection of immunoglobulins refer to passive immunity, where antibodies from another source are given to an individual, rather than the individual’s immune system producing its own antibodies. Maternal antibody transfer also falls into the category of passive immunity, as it involves the transfer of antibodies from mother to child during pregnancy or breastfeeding, providing temporary protection. Blood transfusions can also involve the transfer of antibodies but do not stimulate the recipient's immune system to generate its own response. Therefore, they are not considered a form of active immunity.