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    (C) Lights travels at a speed which is about a million times faster than the speed of sound. You can get some idea of this difference by watching the start of a race. If you stand some distance away from the starter, you can see smoke from his gun before the sound reaches your ears. This great speed of light produces some strange facts Sunlight takes about 8 minutes to reach us If you look at the light of the moon tonight, remember that the light rays left the moon 1.3 seconds before they reached you The nearest star is so far away that the light that you can see from it tonight started to travel towards you four years ago at a speed of nearly 2 million km. per minute. In some cases, the light from one of tonight's stars had started on its journey to you before you were born. Thus, if we want to be honest, we can't say, "The stars are shining tonight" We have to say instead, "The stars look pretty They were shining four years ago, but their light has only just reached the earth." 48．Light speed is sound speed A．as fast as B．a million times slower than C．about millions of times faster than D．about a million times faster than 49．If you stand 200 metres away from a man who is firing a gun to start a race, you will find out that A．you can hear the sound before you see the smoke B．the sound does not travel as fast as light C．the sound will reach you before the man fires D．sound travels about a million times faster than light 50．Sunlight obviously than the light of the moon A．has to travel a greater distance B．moves less quickly C．travels much more quickly D．is less powerful 51．The scientific way of saying "The stars are shining tonight" should be A．the stars have been shining all the time B．the stars seen tonight will shine four years later C．the stars were shining long ago but seen tonight D．the starlight seen today could be seen four years ago 【查看更多】

     

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    根据句意和首字母提示，补全单词，有的单词要作适当变化，完成句子.

    When the t　　 lights are red, you must stop and wait.

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    根据句意和首字母提示，补全单词，有的单词要作适当变化，完成句子.

    When the t　　 lights are red, you must stop and wait.

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    Look at the picture, and complete the word.

    Look at the t　　　 lights. They are red. I think you must wait.

     

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    根据对话内容，从下面方框中选择适当的单词或短语填空，使对话内容完整正确，

    A：Hey! I met a student from a green school in Dalian．

    B：A green school? 　　1　　is it?

    A：It is a school which supports the protection of the environment．In fact, there are　　2　　green schools in China．It's wasteful to throw away glass, paper and metal,　　3　　every class in such schools collects waste that can be used again and then sells it for recycling(再利用)．

    B： Great! What else do they do?

    A： They also save energy and tricycle things at home, such as　　4　　lights and saving water．

    B： If everyone tries to protect the environment, we will make the world much better．

    A： I agree．If we don't, the future is　　5　　．

    B： Anyway, public concern over the environment has greatly increased．There is hope for the future．

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    根据短文内容及首字母提示填写所缺单词

    　　This is a street crossing(十字路口)．There are red and g　　1　　 lights at each corner(交叉路口)．Drivers must watch the light c　　2　　．

    　　When there is a green light, the cars may go on．When there is a red light，the cars must s　　3　　．They must wait u　　4　　 the red light changes to green．Then they can go on．Sometimes the cars want to make a right t　　5　　 or a left turn．They can make a r　　6　　 turn when the light is green or red．But they must wait until the green light is shining if they want to turn l　　7　　．

    　　Some people are color blind(色盲)．They cannot see the d　　8　　 between red and green．These people must not d　　9　　, or else there will be accidents(事故)．We must keep our streets s　　10　　．

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