using fur to trap air for warmth cracking open clams with a rock nursing its young for six months closing its ears under water
I gave my students this multiple choice question: Which sea otter behavior is learned?

Only one answer is correct among these 4 choices:
- using fur to trap air for warmth
- cracking open clams with a rock
- nursing its young for six months
- closing its ears under water

Could you tell me which one is correct?

cracking open clams with a rock