A little boy, Tommy, is walking home by moonlight (月光).He feels another little boy is coming behind him. The boy stops a minute to listen, looks here and there, and then he says to himself，“Tommy, run quickly.”He runs quickly and gets to Mr. Green’s garden. He still(仍然) feels a boy is running after him. Tommy runs home quickly. He goes in and closes the door. He turns on the light. He looks out of the window and doesn’t see anybody. But he knows that the little boy always comes after him when he goes out in the evening by moonlight. Can you guess what is it? It’s a shadow.