Suggested answers to Exercise 3：

　　1，4，3，5，2，6

　　USING LANGUAGE

　　Listening and discussing

　　LISTENING TEXT

　　THEORIES OF GRAVITY

　　Michael Jones of the New Space Magazine is talking with space traveller Li Yanping about changes in the theory of gravity.

　　LY＝Dr Li Yanping　MJ＝Dr Michael Jones

　　Part 1

　　MJ：Hello，Dr Li Yanping.It's so good of you to talk to me.Some students ask us why things always fall back to earth if you throw them up in the air.Could you explain it?

　　LY：Well，at first people thought it was because the earth was the centre of the universe.Of course that was wrong.One day Isaac Newton watched an apple fall to the ground.He said that something else must be pulling the apple back to earth.He called it "gravity"．

　　MJ：I see.Did people accept his idea?

　　LY：They did.Later they worked out that bigger objects(like the sun)have stronger gravity than smaller objects(like our planets)．If you're travelling in deep space，you couldn't fall back to the earth.You're just too far away.

　　Part 2

　　MJ：Does it mean there's no gravity in space?

　　LY：No.In a spaceship you would feel the pull as it got closer to such an object.You would travel faster and faster towards it.

　　MJ：Until you hit it?

　　LY：Not exactly.You may pass it very fast and then it would throw you out into space again.After that you would slow down to the usual speed.

　　MJ：How do you know this?

　　LY：In 1905 Einstein said that in space large objects make space­time bend；the larger the object，the further space­time bends.So time goes slower in very strong gravity.

MJ：What about black holes?