Akio just got over having the flu. His brother just got the flu. His parents are not worried about Akio getting it again because he
built up an immunity to this flu strain.
Which explains the type of immunity he built up?
active because he built up antibodies due to exposure to the flu
active because his parents vaccinated him against the flu
passive because his mother passed on the flu antibody
passive because he had antibodies added to his blood