The food of Galapagos finches with well-defined beaks is () A. Insects B. Seeds C. Fruits D. Immortals.

Galapagos finches are a unique bird group, isolated in the uncompetitive Galapagos Islands and Corcos Islands, and adapted to radiation in several niches, which provided evidence for Darwin's theory that "species are not immutable". Long-billed American finches mainly eat cactus, because there are thorns on the surface of cactus, and long-billed finches can peck at the flower powder and fruit of cactus more conveniently; American finches with thick beaks mainly eat seeds, because such beaks are strong and can bite through the shells of hard seeds; Most other people eat insects. These characteristics are the result of long-term natural selection.

So choose: C.