Even if you are a good high-jumper, you can jump only about seven feet off the ground. You cannot jump any higher because the ea

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问题     Even if you are a good high-jumper, you can jump only about seven feet off the ground. You cannot jump any higher because the earth pulls you hard. The pull of the earth is called gravity.
    You can easily find out the pull of the earth. If you weigh yourself, you will know how much gravity is pulling you.
    Since there is gravity, water runs down hill. When you throw a ball into the air, it falls back down. Because of gravity, you do not fall off the earth as it whirls(旋转)around.
    Then, can we get away from the earth and go far out into space? Now you can do it, because spaceships have been invented. Then spaceship will go so fast that it can escape the earth’s gravity and carry you into space.  
When you slip you always fall to the ground because______.

选项 A、the earth always turns round
B、the earth has gravity
C、the earth’ s gravity is greater than your weight
D、you are careless

答案B

解析 事实细节题。根据第三段可知,因为地球上存在重力,当你滑倒的时候,你总是会倒在地上。而这与你的体重并无关系,故选B。
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