____________________________ develops when the body is exposed to antigens from invading pathogens.

Active immunity develops when the body is exposed to antigens from invading pathogens. This type of immunity occurs as a result of the immune system's response to a specific pathogen, which involves the production of antibodies by the body’s own immune cells. When pathogens enter the body, they present antigens that trigger an immune response, leading to the creation of memory cells that will recognize and combat the pathogen in future encounters.

Active immunity can occur naturally when a person gets an infection and recovers, or it can be acquired through vaccinations that present harmless forms of the pathogen or its antigens, stimulating the immune system to respond and build protection.

In contrast, passive immunity involves the transfer of antibodies from one individual to another (such as through maternal milk to a nursing infant) and does not involve the individual's own immune response. Natural immunity refers to immunity gained through natural exposure to pathogens, which may overlap with active immunity but is not as broad a term. Adaptive immunity encompasses the specific immune responses against pathogens and is closely related to active immunity but is a broader classification that can include both active and passive responses.