Answer: When B cells and T cells are first activated by a pathogen, memory B-cells and T- cells develop.
Throughout the lifetime of an animal these memory cells will “remember” each specific pathogen encountered, and are able to mount a strong response if the pathogen is detected again. This type of immunity is both active and adaptive.
Active immunity often involves both the cell-mediated and humoral aspects of immunity as well as input from the innate immune system.
Explanation: Hope it Helps