Which Observation from Darwin's Stay in the Galápagos Islands Was

Multiple Choice

Which observation from Darwin's stay in the Galápagos Islands was most instrumental toward his eventual development of evolutionary theory?

A) Animal species on the islands were endemic to the islands but were similar to species on the South American mainland.
B) Animal species on the islands were endemic to the islands but were similar to species on the European mainland.
C) Species of the temperate regions of South America were more similar to those of tropical South America than they were to temperate European species.
D) Species of the temperate regions of South America were more similar to temperate European species than they were to those of tropical South America.
E) A catastrophic earthquake could almost instantaneously wipe out many species.