Cuban Tree Frogs Are a Much Greater Problem in the United

Cuban tree frogs are a much greater problem in the United States than in Cuba; what hypothesis best suggests why?

A) Foods available to the tree frogs in the United States have a higher nutritional quality and represent an increased carrying capacity for frog populations.
B) The United States has a cooler climate, which allows the tree frogs to be more active and aggressive.
C) Tree frogs were introduced without the natural biological constraints they experience in Cuba and have become much more numerous in the United States.
D) Natural selection gradually improves a species competitive advantages; the immigrant frogs simply reflect these evolutionary changes.