C) option is correct
Step-by-step explanation:
Allopatric speciation is a type of speciation in which formation of species occurs due to geographical barriers like continental drift (partitioning of continents), origin of mountains, origin of ocean and origin of volcano
Allopatric speciation has least character displacement
The fixation of somatic modification into genetic modification is called character displacement upon change in environmental condition and niche overlap ecotype are examples of character displacement
In the given example, two forms of population were unable to interbred when their expanding ranges met, it would be an example of allopatric speciation