20,000 years ago, two populations of the black-tailed rats became separated from each other by the formation of a large canyon, thus preventing their interbreeding. the condition described is
a) mass extinction.
b) selective breeding.
c) adaptive radiation.
d) geographic isolation.

The environment changes all the time. Animals of course have no control of it. When geographic changes happen (large canyon forming, volcanoes erupting, glaciers melting) and the population of species are isolated and not able to interbreed, the condition is geographic isolation. 

b

explanation: