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    Thousands of years ago，people didn’t know why sometimes the moon is full and sometimes it is crescent（弯曲）shaped，and even sometimes it can’t be seen at all．The moon was a great mystery（谜）to them．They made up stories about the great light in the night sky．They thought there was a god up there who was in charge of（掌管）the moon。They called the god，“Moon God”．

      In fact the moon is the Earth’s satellite（卫星）．Many planets have a satellite，and some have many．Our moon travels around the Earth once a month．It’s much smaller than the Earth and gravity（引力）pulls it．

    In most nights the moon is the brightest thing in the sky．This is because it reflects（反射）light from the sun．It doesn’t shine itself．

    What we see of the moon changes from night to night．Its changing shapes are called phases（盈亏）．The pictures of the moon’s phases show the shapes of the shining part of the moon that people see in its different phases．

    When the moon is between the sun and the Earth，we can’t see the moon at all．This is called a“new moon”．

    When the moon is behind the Earth and the sun shines on it，there is a“full moon”．

    Thanks to space travel，people now know more about the moon．Humans have even visited it．They know that there is no air，no water or life there．But there is much sunlight and natural resources（资源）．These can be very useful to us．Some scientists say，with the help of modem technology，more and more people will be able to go to the moon，even live on it．Maybe it will be some people’s second home in the future．

（The changing positions of the moon’s phases）  （The pictures of the moon’s phases）

1．In the third sentence of Paragraph I“They made up stories about the great light in the night sky”，“the great light”refers to _____________．

2．Why is the moon very bright in most nights?

3．We can see the“full moon”____________times a year．

4．将画线的英语句子译成汉语。

5．Which of the pictures a，b，c，d，e is of a“new moon”?