A Certain Species of Tree Frog Was Able to "Re-Evolve

A certain species of tree frog was able to "re-evolve" teeth on their lower jaws because

A) mutations are more likely to occur in regions of the genome that affect jaw formation.
B) the mutations that led to the "toothless" allele were corrected over time by DNA repair proteins.
C) organisms tend to encounter the same environmental pressures every few million years.
D) the genes involved in tooth formation are still in the frog's genome.