Which of the following factors would not contribute to allopatric speciation? a) the isolated population is exposed to different selection pressures than the ancestral population. b) a population becomes geographically isolated from the parent population. c) gene flow between the two populations is extensive. d) the separated population is small, and genetic drift occurs. e) different mutations begin to distinguish the gene pools of the separated populations.

Allopatric speciation can be defined as the speciation that occurs when the populations of the same species are isolated from one another due to some geological barrier. When the isolated population is put under different selection pressures, it will lead to the evolution of the genetic pool in the isolated population and speciation will occur.

Similarly, geographical isolation from the parent population, genetic drift, and different mutations in the isolated population will lead to speciation. However, if there is continuous gene flow between the isolated and parent population, then the speciation will not occur.

Hence, the correct answer is 'Option C'.