When the 8-Year-Old Asks the Nurse How She Got the Antibodies

When the 8-year-old asks the nurse how she got the antibodies that kept her from getting whooping cough, the nurse explains that those "shots":

A) Were borrowed antibodies from another person who had whooping cough
B) Gave her a "tiny" case of whooping cough and then she made her own antibodies
C) Strengthened antibodies she was born with
D) Are only temporary borrowed antibodies and she needs to have another "shot" every 5 years