A subset of a population of birds leaves its habitat on the mainland and colonizes a nearby island. The birds, after a period of time, become reproductively isolated. The island sinks and the population of birds that lived on the island returns to itsoriginal habitat. Which of the following statements about these bird populations is true?

A. The birds were separated by a vicariance event
B. The populations were sympatric while they diverged
C. The populations will not be able to interbreed because they are different species
D. The populations will be able to interbreed even though they are different species