Answer to Question 1
b
Answer to Question 2
In active immunization, the individual is exposed to an antigen in a harmless form and produces antibodies as well as activated T and B cells and memory cells. The memory immune response, initiated upon exposure to the pathogen or a booster, prevents infection and provides additional antibodies and memory cells. In some cases, such as influenza, the residual antibodies are more important than the memory response due to the short incubation period of the disease, and more frequent vaccinations are often required to maintain the antibody level.