阅读短文，填空。 Birds Although (虽然) all birds may not look the same, all birds have certain things in common (共同点). All birds are warm-blooded. This means that their body temperature always stays the same. Birds breathe with lungs. A bird's body is covered with feathers. All birds have two wings. Baby birds are hatched from eggs. Birds can see very well. They can't move their eyeballs like people do, so they have to turn their heads to look at something. Birds' ears are round holes on the sides of their heads. There are about 9, 000 kinds of birds in the world. 1. There are over ____________ kinds of birds in the ____________. 2. Birds don't have ears like people do. Their ears are ____________ ____________ on the sides of their heads. 3. Birds can't move their ____________ so they have to turn their ____________ to look at something. 4. Birds have hundreds of ____________ but only two ____________ and ____________ wings.