We are all familiar with magnets. The Chinese knew about them in the eleventh century. But the earth itself is also a magnet. No one really understands very much about the earth’s magnetism, although many people have written about it. Scientists believe the center of the earth is like a large magnet, giving out a steady magnetic force. This slowly moves away from the center and up to the surface. By the time it reaches the surface the force is really very weak.

New word(s): magnet（磁铁）
(83 words)

　　Which of the following is the best title of the passage?
　　 A) The Functions of Magnetic Force.　　　　
　　 B) The Earth’s Magnetism.　　　　
　　 C) The Center of the Earth.　　　
　　 D) The Discovery of the Earth’s Magnetic Force.
　　　

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