Answer: B. species A and species B can no longer exchange genes.
Step-by-step explanation:
Geographic isolation is a kind of reproductive isolation in which the organisms of the same species are separated by a geographical barrier like flood, river and others. The separated members of the same species are unable to copulate and they develop new traits according to the new environment. This leads to formation of new species and the process is called as speciation.
According to the given situation, the two species A and B are geographically separated thus they will not be able to exchange their genetic materials due to geographical barriers.