Galpagos medium ground finches are found on Santa Cruz and San Cristbal islands, which are separated by

Galápagos medium ground finches are found on Santa Cruz and San Cristóbal islands, which are separated by about 100 km of ocean. Occasionally, individuals from either island fly to the other island to stay. This can alter the allele frequencies of the population through which of the following mechanisms?

a. Natural selection

b. Genetic drift

c. Gene flow

d. Mutation