The answer is d. random change in gene frequency
Genetic drift is a change in the frequency of alleles in a population as
a result of random sampling of organisms. For example, imagine you have two different alleles in the population responsible for white and purple color of a flower. Their allele frequencies are 0.6 for white flowers and 0.4 for purple flowers. After some change in the environment, only purple flowers survive. They will reproduce, and in the population there will be only purple flowers. The population for these flowers will increase from 0.4 to 1.
