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  3. Periodic realignment of the Earth’s magnetic field occurs two ways: t

Periodic realignment of the Earth’s magnetic field occurs two ways: t

游客2024-01-11  29
问题            Periodic realignment of the Earth’s magnetic field occurs two ways: the
       first, "field regeneration", or the creation of new magnetic fields from the
       ambient geomagnetic field, takes place because magnetic field lines are trapped
Line    in effective electrical conductors. The field is trapped in molten iron which
(5)      moves in response to the forces imposed upon it and as the core moves, the field
       lines are stretched and twisted, creating a new magnetic field. The second
       process is the diffusion of the magnetic fields: in the same way that a drop of
       dye will soon diffuse throughout a swimming pool, a concentration of magnetic
       field lines diffuses throughout the planet’s outer core. On the large scale of
(10)     stars and planets, the field lines are caught up in the fluid motion and distorted,
       generating a new magnetic field before diffusing away. This rarer type of field
       reversal is likely caused by unexplained larger changes in the flow in the outer
       core, though scientists have suggested such fluctuations may simply be extreme
       examples of fluctuations in the dynamo processes-an El Nino in the weather of
(15)     the outer core. [br] The passage is chiefly concerned with
选项 A、offering an explanation of the process that causes a phenomenon, and a counter-explanation
B、demonstrating how two processes act in symbiotic coordination in causing a phenomenon
C、establishing how one process causes a phenomenon which is resisted by a second process
D、explaining two separate processes which cause a mostly identical phenomenon
E、outlining the essential differences between two distinct phenomenon that issue from a single cause
答案 D
解析
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