If the Original Finches That Had Been Blown Over to the Galápagos

If the original finches that had been blown over to the Galápagos from South America had already been genetically different from the parental population of South American finches, even before adapting to the Galápagos, this would have been an example of

A) genetic drift.
B) the bottleneck effect.
C) the founder effect.
D) genetic drift and the founder effect.
E) all three of these.