Periodic realignment of the Earth’s magnetic field occurs two ways: the first, "field regeneration", or the creation of n

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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.
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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