They all have fur. They all have backbones. They all are warm-blooded. They all have young that look like the adults.
I gave my students this multiple choice question: What do all vertebrate animals have in common?

Only one answer is correct among these 4 choices:
- They all have fur.
- They all have backbones.
- They all are warm-blooded.
- They all have young that look like the adults.

Could you tell me which one is correct?

They all have backbones.