Which scenario is an example of a functional adadption ?

The correct answer is D.
In biology, adaptation refers to any structural modification or behavior that will make it easy for an organism to survive in its environment. There are three basic types of adaptation, these are functional, structural and behavioral adaptation. Functional adaptation refers to any adaptation that will make an organism to survive in its environment based on the functions of its body parts. In the question given above, flounder was able to avoid been eaten by predators because its color and shape make it possible for it to camouflage when predators are around.

This is the most closely resembles the model.