<span>In the past, human populations were controlled by </span>Disease and Famine
Because an antibody is "made" relative to the antigen, but kept at low levels when you are exposed the first time ("primary immune response"). The second time you're exposed to the same antigen, memory cells recognize it and the body produces a high level of antibodies, and the level of antibodies usually remains higher for a longer time ("secondary immune response"). This is your basic immune response (primary and secondary).
This explains exactly why vaccines are effective to extremely effective.
The question is asking to choose among the following choices that states the length of time that an organism expected to live, and base on my research and further investigation, I would say that the answer would be A. life span. I hope you are satisfied with my answer and feel free to ask for more
