SECTION 3Directions: Each passage in this group is followed by questions based on its cont
SECTION 3
Directions: Each passage in this group is followed by questions based on its content. After reading a passage, choose the best answer to each question. Answer all questions following a passage on the basis of what is stated or implied in the passage.
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
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
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