Its D becuase
1. the question says 'explain how these animals can be used to illustrate DARWIN/WALLACE'S theory of evolution by natural selection and isolation'. AN ORGANISM CHOOSING TO CHANGE ITS BEHAVIOUR TO SUIT ITS ENVIRONMENT IS NOT EVOLUTION. Example, the world floods, elephants aren't just going to survive by choosing to swim, they will have to EVOLVE and develope gills, fins, etc. Woah, that example suks but u get the picture.
2. D is an example of Darwin and Wallace's theory, i.e. convergeant evolution, although they are different species and are in different parts of the world, they have evolved in the same way due to their similar environments. Much like the dolphin and shark; not the same species, but look the same due to the evolutionary convergeance that has occured due to living in the ocean. C is not an exaple of darwin and wallace's theory, as said by others b4, thats a Lamarkian view.
3. Your wrong.