The transition of the Earth’s magnetic field is possibly caused by _____.
A、the flows of melted iron inside the Earth
B、the periodical movement of the Earth
C、the mechanical energy of the solar system
D、the force coming from outer space
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试题解析
文章最后一段:谁也不能准确地知道为什么地球磁场会周期性转换,但是科学家说其原因可能在于地壳中融化了的铁的无序流动,它们看起来就像木星上组成云的气体一样。