If the finches that colonized the Galápagos from South America had different allele frequencies when compared to the parental population of South American finches, even before adapting to the new environmental condition on the Galápagos, this would have been an example of

genetic drift.

bottleneck effect.

founder effect.

A and B only.

A and C only.

This is an example of founder effect and genetic drift. The right answer is A and C only

Explanation:

Genetic drift is a mechanism in the process of evolution in which the sampling error ( change in allele frequencies  of population occur).

Here Genetic drift will lead to founder effect as colonization of species has taken place.

When a small population forms colones and does not contain the genetic diversity present in parental population. The  movement from larger population to smaller population and having different gene frequencies is called Founder effect. The change in the alleles would lead to generation of same alleles and hence they will experience drift over a large period of time.