A) Genetic drift is the random increase or decrease of genes in a population. Natural selection is not random.
Genetic drift is the change in the frequencies of alleles in a population due to chance events (random survival). Genetic drift exhibits strong effects in small populations and plays a smaller role the larger the population gets. Natural selection is the non-random change in the frequency of alleles in a population over time, because the change in frequency of the alleles is dictated by the different relative fitnesses that different alleles confer.