A. a geographic separation occurs between subpopulations
Explanation:
Allopatric speciation, which can also be called geographic speciation, is a type of speciation that involves the isolation of biological populations of the same species. This isolation is caused by geographical changes which include, formation of islands, mountains, and bodies of water. Social changes, brought about by human activities such as urbanization and agriculture, also aids Allopatric speciation.
The isolation of subpopulations from each other will lead to the gene flow being interfered or hindered.
