Every object has weight. But the center of its weight is not always in the middle of the object. If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity is high. But if the bottom is heavier, it won’t fall easily. Then we say that its center of gravity is low.

Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB).

Now look at the second picture. There is some heavy iron in the bottom of this box. It will not fall, because its center of gravity is above its bottom.

1.If the bottom of an object is ______ its top, it will fall over easily.

A. lighter than　　 B. heavier than　　 C. no heavier than　　  D. as heavy as

2.Please point out which box will not fall.

3.The main idea of the passage is _________.

A. why things fall over　　　　         B. a low center of gravity

C. a high center of gravity　　             D. that everything has weight

Every object has weight. But the center of its weight is not always in the middle of the object. If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity is high. But if the bottom is heavier, it won’t fall easily. Then we say that its center of gravity is low.
Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB).
Now look at the second picture. There is some heavy iron in the bottom of this box. It will not fall, because its center of gravity is above its bottom.

【小题1】If the bottom of an object is ______ its top, it will fall over easily.

　　Every object has weight. But the center of its weight is not always in the middle of the object, If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity（引力）is high. But if the bottom is heavier, it won't fall easily. Then we say that its center of gravity is low.

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A．the top of the tower is heavier than its bottom

B．the bottom of the tower is not heavier than its top

C．its center of the gravity is still above the line of its bottom

D．its center of the gravity is not above the line of its bottom

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A．The center of the weight is always in the middle of the object

B．The center of the weight is always on the object

C．The center of gravity is not always in the middle of the object

D．The center of the gravity is always high

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Disasters happen all the time somewhere in the world. Are you ready if one hits your neighborhood next week? Find out what you need to do now before it is too late. Let’s take an earthquake for example.

    During an earthquake, get under a strong object like the kitchen table. Don’t leave the building during the shaking, or you might be hurt by falling objects from the outside of the building.

    When you are in bed during the night and an earthquake happens，simply roll off the bed. There will be a safe void around the bed.

    If you are watching TV and you cannot easily run away by getting out through the door or window, then lie down and curl up(蜷伏) next to a sofa, or a large chair.

    Never go to the stairs. The stairs are likely part of the building to be broken. Even if the stairs are not destroyed by the earthquake，they may fall down later when people run down.

    Try to get into an open area away from trees，buildings，walls，advertisement boards and power lines if you are outdoors.

    If you are driving when an earthquake suddenly happens，just stay in your car until the shaking ends. However, if the footbridge falls and breaks your car，get out of it and sit or lie next to it. All the broken cars have voids 3 feet high next to it.

1. What should you do if you are in a building when an earthquake happens?

   A. Rush out quickly            B. Sit in the kitchen

   C. Stay below strong objects      D. Go down the stairs

2.The underlined word “void” in Paragraph 3 means“_______”.

   A. space          B. seat            C. distance         D. sign

3. When you are outdoors during an earthquake，you should go to _______.

4. If you are inside a car when there is a sudden earthquake，you should _______.

A. get out of it      B. keep inside it   C. move away fast   D. stay under the footbridge