Answer
Genetic drift involves random chance alterations of allelic frequencies in small populations, usually greatly reducing or eliminating one or more alleles. In contrast, gene flow involves individuals moving into a population, whatever its size, usually increasing genetic variation (though lots and lots of one homozygous genotype flowing into a population could reduce variation).
Work Step by Step
Review the definitions in the text and use your imagination to see that genetic drift usually makes a population more homogeneous, while gene flow would usually bring more (and, perhaps, novel) alleles into the population.
