Everybody has a home. People have homes. Animals have homes, too. People live in different kinds of homes. Animals also have different kinds of homes. Some animals live in holes under the ground. The woodchuck   lives under the ground. Its home has two doors. If any enemy comes through one door, the woodchuck goes out of the other. Some animals live in holes in trees. Some squirrels  build nests high in trees. Some birds live in holes in trees. Most of the birds live in nests . Crows  build their nests high in trees. But hawks  build their nests high in the mountains. Some animals even carry their homes on their backs . The passage is about   _  .
some trees some animals and birds animals' homes different animals