In his observations of the tortoises on the Galápagos Islands,Darwin concluded that

A)long-necked tortoises acquired their long necks by stretching to reach vegetation.
B)those tortoises were not related to tortoises on the mainland.
C)each island species was derived from a different mainland ancestor.
D)where vegetation was sparse, long-necked tortoises were favored because they could reach higher to get their food.
E)short-necked tortoises had resulted because of spontaneous generation.