Answer:
d. geographic isolation
Step-by-step explanation:
Geographic isolation is the type of isolation that has occurred in the Galapagos Islands with the different tortoise species. This type of isolation occurs when a species is separated by a physical barrier, such as a mountain range, a body of water, or an area of land. In this case, the different islands of the Galapagos served as the physical barrier that separated the tortoises, preventing them from interbreeding and eventually leading to the development of separate species.