| There are some earth phenomena you can
count on, but the magnetic field, someday is not of them. It fluctuates in
strength, drifts from its axis, and every few 100, 000 years undergo a dramatic
polarity reversal-a period when north pole becomes south pole and south pole
becomes north pole. But how is the field generated, and why is it so
unstable Groundbreaking research by two French geophysicists promises to shed some light on the mystery. Using 80 meters of deep sea sediment core, they have obtained measurements of magnetic-field intensity that span 11 polarity reversals and four million years. The analysis reveals that intensity appears to fluctuate with a clear, well-defined rhythm. Although the strength of the magnetic field varies irregularly during the shout term, there seems to be an inevitable long term decline preceding each polarity reversal. A. Polarity Reversal: A Fantastic Phenomenon of Nature B. Measurement of the Earth’s Magnetic-Field Intensity C. Formation of the Two Poles of the Earth D. A New Approach to the Study of Geophysics [单项选择]Can you imagine how you would feel if you fell dangerously ill and could not reach or call a doctor Millions of people (1) the world are in this unfortunate (2) , living in distant places (3) there are no railways, no proper roads and no telephones. Thousands of (4) are lost every year (5) could have been saved if medical attention (6) in time. (7) today help could be brought quickly and easily (8) many of these people (9) full advantage was taken (10) the aeroplane. (11) country has proved this (12) than Australia. The Australians (13) greater use of the aeroplane than any (14) people in the world. In no other country (15) the total number of miles flown by the (16) person so high. In fact, it has been (17) that Australians jump into planes (18) people in other countries jump into trains and buses. It is not surprising,
B. but C. and D. unless 我来回答: 提交
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