Final answer:
Allopatric speciation requires geographic isolation, where members of a species are separated by physical barriers and evolve into distinct species due to the lack of interbreeding. The option (B) is correct.
Step-by-step explanation:
Allopatric speciation requires geographic isolation. This form of speciation occurs when members of a species become separated by geographic barriers such as mountains, rivers, or oceans, and evolve independently over time. An illustrative example is how different species of squirrels evolved on the two sides of the Grand Canyon due to the barrier it presents, thus preventing interbreeding and allowing for the development of distinct species.
Isolation leading to allopatric speciation can be the result of many natural events, such as the formation of new rivers or valleys, or long-distance dispersal events like seeds crossing an ocean to an island. The nature of the geographical separation that leads to speciation is entirely dependent on the biology of the organism and its potential for dispersal. For instance, rodent populations divided by a new lake are less likely to continue gene flow, making speciation more probable in their case as compared to flying insects living in separate valleys that can still interbreed. Therefore, option (B) is correct.