Final answer:
The Galápagos Islands were the most influential in shaping Charles Darwin's theories during his voyage on the HMS Beagle, where his observations on species variation played a key role in the development of his theory of evolution. Therefore, the correct option is A.
Step-by-step explanation:
During Charles Darwin's voyage on the HMS Beagle, the stop at the Galápagos Islands proved to be the most influential in his development of the theory of evolution. While visiting these Islands, Darwin made crucial observations regarding the distinct variations in species on the different islands, such as the unique beak shapes of the finches, leading him to contemplate the origin of species. The Galápagos Islands are a group of 16 volcanic islands located approximately 600 miles off the west coast of South America. The diversity of life and the varying adaptations of organisms like finches, iguanas, and tortoises on these islands inspired Darwin to formulate his ideas on natural selection and evolution.