A crow  is about twenty inches  long and black all over. Crows are dirty birds because they live on bad food. Crows eat a lot of waste food. In this way they are more useful to us than any birds. They clean up the dirty things in our streets. Crows are always hungry. They look for food all day, and in the evening you can see them in large numbers flying back to their nests  in the trees. They sleep there at night. Crows are much noisier than other birds. Very often a large number of crows will get together on one house and talk. Sometimes they talk together, and sometimes they do it by turns  like human beings . It is easy to tell  from crow's sound if they are pleased or angry. Perhaps crows talk a lot because they are friendly birds. A pair of crows will live together all their lives, and if one of them dies, the other one becomes very sad and quiet for the rest of its life and some time later it dies too. Crows "live on bad food" means "   _   ".
Crows eat old bad food. Old bad food is crows' nests. Crows make their nests on old bad food. Crows sleep on old bad food.