Which of the following statements is true? a. gene flow and natural selection always result in evolution. b. gene flow usually increases the genetic differences between two populations. c. according to natural selection, organisms with poor adaptations will never reproduce. d. since genetic drift is random, it does not always favor the "healthier" or "better" organisms.

The correct answer is option D, that is since genetic drift is random, it does not always favor the better or healthier organisms.  

A mechanism of evolution in which the frequencies of alleles of a population change with generations because of sampling error is known as genetic drift. It takes place in all the populations of non-infinite size, however, its influences are strongest in small populations.