Question

Fish, amphibians, reptiles, birds, and mammals have similar embryos.
They all start with gill slits. Fish and some amphibians grow to have gills. Some amphibians, reptiles, birds, and mammals develop lungs to breathe air.
They all start with tails. Fish, some amphibians, reptiles, and birds grow tails. Humans do not keep their tails.
Fish and reptiles develop scales. Amphibians, birds, and humans have skin. Birds have feathers, and humans have hair.

Which two animals exhibit the most linear relationship?

1. amphibians and fish

2. birds and humans

3. amphibians and reptiles

4. birds and reptiles