because fish, penguins, and dolphins are aquatic animals. It can't be A. because if it were vestigial it would be useless. It can't be B even though it does seem like the right answer because the are all aquatic. It can't be C. because it would been that the same species would have the same niche which is not possible. It can't be D. because every organism is evolved from a common ancestor.
It's aimed at helping people to become aware of when they make negative interpretations, also it helps people to develop new ways of thinking which will lead to reducing distress.