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举一反三
【单选题】第三篇 There are some earth phenomena you can count on, but the magnetic field, some say, is not one of them. It fluctuates in strength, drifts from its axis, and every few 100,000 years un...
A.
its identification of the origin of the earth’s magnetic field
B.
the way the earth’s magnetic intensity is measured
C.
its explanation of the shift in the earth’s polarity
D.
the way the earth’s fluctuation rhythm is defined