但是偶尔这偶极场会转换极性——南极和北极倒转，这个过程似乎需要几千年的时间。
But occasionally this dipole field switches polarity north and south reverses, and this process seems to take a few thousand years.
但是偶尔这偶极场会转换极性——南极和北极倒转，这个过程似乎需要几千年的时间。
But occasionally this dipole field switches polarity north and south reverses, and this process seems to take a few thousand years.
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