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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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 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

“Mum, I want to make you a bet,” I said. “If I go a whole year without TV, will you give me a hundred dollars?”　　
“Well, if you can   1  do it, …”
“Of course I can,” I replied, trying to convince   2 .
In fact, all this started from my   3  of a picture in the newspaper. I couldn’t bear to look at that boy. He said that he had   4  one year without TV for a hundred dollars,   5 me with mocking eyes. It seemed he was saying, “I did it,   6  you can’t!”. I glared at the boy’s face.
That year I did a lot of things. For example, my father taught me to   7 , which became my favorite sport.   8  winter afternoons snowball wars with my neighbors offered daily drama. I went on bike trips with my friends and swam as much as a fish.　　
It was unbelievable how much   9  I had without TV. I learned so many new games. I guess the   10  thing I learnt, though, was self-motivation(上进心).　　
I started to do my homework. I went from a D student to an A student within a couple of   11 .　　
I used to   12  reading if there were no   13 , but now I began to read and enjoy it. I could arrange off all the pictures just the way I wanted them—my own little TV, right   14  my head!
I’m surprised what I did. I got a lot more from the   15  than just the 100 dollars!