Most causes of speciation are relatively slow, in that the differences separating species take many generations to accrue and establish reproductive isolation. Which of the following is most likely to produce a species in just a few generations?
a. Genetic drift
b. Behavioral isolation
c. Reinforcement
d. Founder effect
e. Polyploidy

Genetic drift produces a species in just a few generation.

Explanation:

Genetic drift means change in the gene frequency in a population due to random sampling of an organism.The allele of the sample in the parents has a role that determines the survival and reproduction of the organism.Allele frequency is the copy of gene which shares a particular form.Thus those speciation which occur due to genetic drift will produce species in just few generations.

The effect of genetic drift is larger and is acting on neutral mutation.