Polio Is a Disease That Was Almost Eradicated, but There

Multiple Choice

Polio is a disease that was almost eradicated, but there are still new cases that appear due to the failure to immunize all children. Researchers keep close tabs on how many new cases of this disease occur each year in the hope that it will soon cease to exist. This enumeration is an example of

A) prevalence.
B) duration.
C) incidence.
D) frequency.