Label each example as either (pi) passive or (ai) active immunity:
a. bill had chicken pox when he was five. he doesn’t catch it again, even when his nephew gets sick with the virus.
b. billy jr gets vaccinated with a live attenuated form of the chicken pox virus. he doesn’t get chicken pox after playing with his infected cousin.
c. bill’s 3 month old daughter is breast feeding. she does not get chicken pox after playing with her infected cousin.

First, let's distinguish active from passive immunity:
- Active immunity occurs in a direct exposure of individuals to live pathogens. The result is a development of a disease. After that, individuals acquire immunity to the disease.
- Passive immunity is induced by vaccines with antibodies for a disease, so the disease does not develop.

a. ACTIVE IMMUNITY - Bill had a disease, so it must be active immunity.
b. PASSIVE IMMUNITY - Bill got a vaccine and a disease did not develop, so it must be passive immunity.
c. PASSIVE IMMUNITY - Although, 3-month-old daughter did not get a vaccine, she has mother's antibodies from the milk so she will not develop a disease.