Both large and small frogs are able to live in the wet climate of the South. Too much moisture is not the problem here, so we don't know how many of each type are in the South. This is why we cannot conclude D.
C is better, because the passage tells us that large frogs can survive in some arid climates while small frogs cannot. Therefore, large frogs can live in more areas of the Yucatán than small frogs.