Active immunity develops when the body is exposed to what?

Active immunity develops when the body is exposed to antigens from invading pathogens. This process occurs when the immune system encounters a foreign element, such as bacteria or viruses, and responds by producing specific antibodies to fight off the infection. Once the body has faced these antigens, it retains a memory of them, which allows the immune system to react more swiftly and effectively in the event of future exposures to the same pathogens.

In contrast, other options such as antibiotics from medications do not trigger the body's immune response but rather provide an external means to combat infections. Vitamins and nutrients, while essential for overall health and immune function, do not directly generate immunity against specific pathogens. Similarly, non-infectious particles in the environment may not engage the immune system in the same way that live antigens do, thus failing to create active immunity.