a wolf's howl an insect's coloring a fish's fin a squirrel storing acorns
I gave my students this multiple choice question: Which of the following is an example of a structural adaptation?

Only one answer is correct among these 4 choices:
- a wolf's howl
- an insect's coloring
- a fish's fin
- a squirrel storing acorns

Could you tell me which one is correct?

a fish's fin