Answer:
The correct answer will be option- D.
Step-by-step explanation:
The speciation or the formation of new species from the ancestral species takes place through three ways: allopatric, sympatric and parapatric way.
The allopatric speciation results in the formation of new species due to the isolation of the population due to geographical barriers. In the given question, the squirrel is not able to mate and produce organisms as they got separated by river or canyon creating geographical barriers.
Thus, option- D is the correct answer.