Some things can carry messages, for example, a sign at the bus stop helps you to know which bus to take. Signs on the door tell you where to go in or out. Have you ever noticed that there are a lot of signs around you and that you receive messages from them all the time?

    People can communicate on many other ways. An artist can use his drawing to tell about beautiful mountains, about the blue sea and many other things. Books are written to tell you about all the wonderful things in the world and also about people and their ideas.

    Books, magazines, TVs, radios and films all help us to communicate with others. They all help us to know what is going on in the world and what other people are thinking about.

地球上所有的生物共有一个家，这就是____ 。它包括____ 、____ 和____ 。