You can’t see any object unless light from that object gets into your eyes．Some of the things you see give off light of their own。The sun，the stars，a lighted lamp are the examples that can be seen by their own light．But most of the things you see are not giving off light of their own．They are just reflecting(反射)light that falls on them from the sun or some other luminous bodies．The moon，for example，doesn’t give off any light of its own．It is not 1uminous．You see it because sunlight falls on it and some of the sunlight reflects on the earth．So moonlight is only second—hand sunlight．
When you look at a book，it sends some of the light which fails on it to your eyes，and you see the book．If light could be kept out from where you’re so that there would be no light from the book to reflect．Then you couldn’t see the book even with your eyes wide open．Light travels so fast that the time in which it travels from the book you’re reading to your eyes is as short as if there were no time at time．Light reaches us from the moon，which is about 380，000 kilometres away，in only a little more than a second．
【小题1】You can see the book because________．

You can’t see any object unless light from that object gets into your eyes．Some of the things you see give off light of their own。The sun，the stars，a lighted lamp are the examples that can be seen by their own light．But most of the things you see are not giving off light of their own．They are just reflecting(反射)light that falls on them from the sun or some other luminous bodies．The moon，for example，doesn’t give off any light of its own．It is not 1uminous．You see it because sunlight falls on it and some of the sunlight reflects on the earth．So moonlight is only second—hand sunlight．

    When you look at a book，it sends some of the light which fails on it to your eyes，and you see the book．If light could be kept out from where you’re so that there would be no light from the book to reflect．Then you couldn’t see the book even with your eyes wide open．Light travels so fast that the time in which it travels from the book you’re reading to your eyes is as short as if there were no time at time．Light reaches us from the moon，which is about 380，000 kilometres away，in only a little more than a second．

1.You can see the book because________．

     A．your eyes are close to it       B．it reflects some of the light

     C．it has light of its own         D．it is big enough to be seen

2.The Chinese meaning of the world“luminous”is close to_______．

     A．闪光的       B．看不见的      C．发光的       D．明亮的

3.________has light of its own．

A．The moon   B．The earth   C．The sun    D．The satellite of Dong Fong Hong

4.Light travels about_________kilometers per second．

    A．300，000      B．100，000      C．400，000        D．190，000

5.Which of the following is TRUE?

    A．All the things you can see give off light．

    B．Light from the book is much faster than that from the moon．

    C．The moment you open your eyes，the light from the book travels to your eyes．

    D．Light travels so fast that there is no time for you to read．

You can’t see any object unless light from that object gets into your eyes．Some of the things you see give off light of their own。The sun，the stars，a lighted lamp are the examples that can be seen by their own light．But most of the things you see are not giving off light of their own．They are just reflecting(反射)light that falls on them from the sun or some other luminous bodies．The moon，for example，doesn’t give off any light of its own．It is not 1uminous．You see it because sunlight falls on it and some of the sunlight reflects on the earth．So moonlight is only second—hand sunlight．
When you look at a book，it sends some of the light which fails on it to your eyes，and you see the book．If light could be kept out from where you’re so that there would be no light from the book to reflect．Then you couldn’t see the book even with your eyes wide open．Light travels so fast that the time in which it travels from the book you’re reading to your eyes is as short as if there were no time at time．Light reaches us from the moon，which is about 380，000 kilometres away，in only a little more than a second．

1. 1.

   You can see the book because________．

   1. A.
      your eyes are close to it
   2. B.
      it reflects some of the light
   3. C.
      it has light of its own
   4. D.
      it is big enough to be seen
2. 2.

   The Chinese meaning of the world“luminous”is close to_______．

   1. A.
      闪光的
   2. B.
      看不见的
   3. C.
      发光的
   4. D.
      明亮的
3. 3.

   ________has light of its own．

   1. A.
      The moon
   2. B.
      The earth
   3. C.
      The sun
   4. D.
      The satellite of Dong Fong Hong
4. 4.

   Light travels about_________kilometers per second．

   1. A.
      300，000
   2. B.
      100，000
   3. C.
      400，000
   4. D.
      190，000
5. 5.

   Which of the following is TRUE?

   1. A.
      All the things you can see give off light．
   2. B.
      Light from the book is much faster than that from the moon．
   3. C.
      The moment you open your eyes，the light from the book travels to your eyes．
   4. D.
      Light travels so fast that there is no time for you to read．

One day when Isaac Newton was reading a book under an apple tree on the farm，an apple fell down and hit him on the head．For most people that would be the end of the story，but not for Newton．Why did the apple fall out of the tree? Does everything fall? What makes things fall? Can anything stop things from falling? Are the sun，moon，and stars falling? Why don't they ever hit the ground?

Newton spent many years answering these questions by thinking and doing experiments．He made up the law of gravity（引力定律）．According to this law everything pulls everything else to itself by a force（力）called gravity．How strong that force is depends on how heavy the things are and how close together．

Newton's law of gravity not only explained how things fall on earth，but how planets move around the sun and how moons move around planets．A friend of his，Edmund Halley，decided to try Newton's theory（理论）on comets（彗星）．People had been studying comets for hundreds of years but failed to understand them，so he decided to study their reports and compare them to Newton's theory．

Up till then people had thought that comets just came and went，and that nobody could know when or why．But Newton's law of gravity gave rules that Halley could use to study the records of comets．He found some reports of a big bright comet that he was sure was the same one，coming back every 75 years．He predicted（预测）when it would come back next．

Halley's prediction came true．Tile comet appeared at the right time as he predicted using Newton's ideas．This was enough to convince anybody who still didn't believe Newton．Halley's Comet has come a few times since then，always right on time．You'll be able to see it on its next trip near the sun and earth when you're old enough to be a grandparent．

1．The passage starts with a story to show _______．

A．it was such a funny one

B．Newton liked to eat apples

C．how much Newton liked reading

D．what led to Newton's discovery of gravity

2．How strong gravity is depends on _______ of the things according the Newton’s theory．

A．color and distance（距离）                      B．weight and distance

C．size and weight                                          D．size and color

3．According to the writer，Newton was especially different from others in that _______．

A．he liked reading under apple trees              B．he liked to find out how things worked

C．he was very quiet and patient                             D．he was so much interested in science

4．The underlined word convince in the last paragraph probably means “make people _______”．

A．believe                 B．doubt                   C．understand             D．relax

5．Which of the following is true about Edmund Halley?

A．He discovered a big bright comet

B．He helped Newton to create his theory．

C．He predicted when the same comet would come back．

D．He studied the comet for 75 years