A Researcher Is Studying Post-Polio Syndrome in American Polio Survivors

A researcher is studying post-polio syndrome in American polio survivors over the age 65. The researcher selects the sample subjects from the eligible subjects in a tristate area where the researcher is able to travel. Which group is the target population for this researcher?

A) American polio survivors over the age of 65
B) American polio survivors over the age of 65 with post-polio syndrome
C) American polio survivors over the age of 65 with post-polio syndrome in the tristate area
D) American polio survivors over the age of 65 with post-polio syndrome in the tristate area who participate in the research study