③ I heard about how the idea of gravity has developed over a long period of time.

　　④ I heard about three scientists and their work.

　　The best answer : ③

　　1. Listen to the tape again and fill in the chart in Ex. 1 on P30.

　　(Note: Astronomers and scientists think that a black hole is a region of space (not a thing) into which matter has fallen and from which nothing can escape - not even light. So we can't see a black hole. A black hole exerts a strong gravitational pull and yet it has no matter. It is only space - or so we think.)

　　Step3.Reading

　　1. Fast reading

　　T: All the three great scientists Newton, Einstein and Hawking played an important role in the development of ideas of gravity. Would you like to know more about gravity?

　　Ss: Yes.

　　T: Is the moon's gravity the same as that of the earth?

　　S1: No.

　　T: Read fast to see how many times would the force of gravity change?

　　S2: Three.

　　2.Careful reading

　　T: What are the three times? How would the force of gravity change?

And how did our weight change?