A)1900.
B)1950.
C)1965.
D)1977.
E)1989.

A)only occurs in a population in which all individuals are immune.
B)occurs in a population in which a large percentage of the population is immune.
C)only provides protection to those that are already immune.
D)is responsible for dramatic increases in childhood diseases.
E)occurs in a population in which a large percentage of the population is immune AND is responsible for dramatic increases in childhood diseases.

A)polio.
B)diphtheria.
C)hepatitis B
D)pertussis.