The evolutionary process where new individuals are introduced to a population, bringing in new alleles and combinations of genetic traits is referred to as gene flow. There is a transfer of genetic materials coming from another population to a new population. This can happen through migration and also called as gene migration. The movement of alleles is important because there is a movement of alleles among different populations.
Genetic drift is is a fluctuation of the frequency of a gene in a population. Non-random mating is is the probability that two individuals will be able to mate that is not true to all the pairs in the population. Natural selection is the adaptation to change of organisms in a certain population.
Answer - A. gene flow