一个物体放在水平地面上，下列关于物体和地面受力情况的叙述中，正确的是______．
A．地面受到向下的弹力是因为地面发生了形变；
B．地面受到向下的弹力是因为物体发生了形变；
C．物体受到向上的弹力是因为地面发生了形变；
D．物体受到向上的弹力是因为物体发生了形变．
地面受到弹力是因为物体发生了形变，而产生了向下压地面的力，故A错误，B正确；
而物体受到向上的力，是因为地面产生了形变，而产生了方向向上的弹力，故C正确，D错误；
故选BC．
| 阅读理解。 | |||||||||||
| George Stephenson was born in 1781 in a poor family. He had to start work when he was only eight. When George was fourteen, he became his father's helper. He spent a lot of time learning about engines. On holidays, he often took engines into pieces and studied each piece carefully. Soon he became a very good worker though he could not read or write. He began to learn the English letters when he was seventeen years old. Every day after he did twelve hours of hard work, he walked a long way to have lessons from a young teacher. On his eighteenth birthday, he wrote his own name for the first time in his life. George invented many things in his life. The train was the greatest one among them. Today when we watch or take trains from one place to another, we will think of this great man ------George Stephenson. | |||||||||||
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