Which of the Following Is an Example of Adaptation

Which of the following is an example of adaptation?

A) A population of finches develops robust beaks in response to a change in food supply.
B) An island population derived from a small group of castaways has an unusually high prevalence of a rare genetic disease
C) A rare mutant allele for a medicinally beneficial chemical is lost in a plant population residing in a tropical forest fragment
D) The last black-footed ferret dies in captivity