Two subgroups of a population separated by a river are rejoined when a drought causes the river to run dry. Assuming that speciation has not yet occurred, what is true about the two subgroups?

A. Speciation will speed up since there will be more competition
between the subgroups.

B. The likelihood that speciation will be completed will decrease.

C. The two subgroups will still be reproductively isolated and unable
to mate.

D. New traits that resulted from mutation will not flow between the
subgroups.