Fish have gills. Fish eat the same food. Fish live in the same area. Fish have the same predators.
I gave my students this multiple choice question: Scientists group animals based on physical features. Trout are classified as fish because of what physical feature?

Only one answer is correct among these 4 choices:
- Fish have gills.
- Fish eat the same food.
- Fish live in the same area.
- Fish have the same predators.

Could you tell me which one is correct?

Fish have gills.