历年试题:GRE试题(一)

历年试题:GRE试题(一)
evidence tracing the solar-activity cycle in the distant
past could be found, it might also resolve an important(35)
issue in solar physics: how to model solar activity. cur-
rently, chere are two models of solar activity. the tirst
supposes that the sun’s internal motions (caused by
rotation and convection) interact with its large-scale
maic field to produce a dynamo. a device in which(40)
mechanical energy is converted into the energy of a mag-
is taken to be self-sustaining, so that the solar-activity
cycle it drives would be maintained with little overall
changc for perhaps billions of years. the alternative(45)
exp)anarion supposes that the sun’s large-sca)e maic
field is a remnant of the field the sun acquired when it
formed, and is not sustained against decay. in this
model. the solar mechanism dependent on the sun’s
maic field runs down more quickly. thus, the char-(50)
acteristics of the solar-activity cycle uvuld be expected to
change over a long period of time. modern solar obser-
vations span too short a time to reveal whether present
cyclical solar activity is a long-lived feature of the sun,
or merely a transient phenomenon.


17. the author focuses primarily on
(a) presenting twopeting scientific theories concerning solar
activity and evaluating geological evidence often cited to support them
(b) giving a brief overview of some recent scientifrc developments
in s’olar physics and assessing their impact on future climatological research
(c) discussing the difficulties involved in linkinl: ter- restrial
phenomena with solar activity and indicating how resolving that issue
could have an impact on our understanding of solar physics
(d) pointing out the futility of a certain line of sci- entific inquiry
into the terrestrial effects of solar activity and rmendine ita
aban- donment in favor of purely physics-oriented research
(e) outlinine the specific reasons why a problem in solar physics has
not yet been solved and faulting the overly theoretical approach of modern
physicists.
18. which of th.e following statements about the two models of solar
activity. as they are described in lines 37-55, is accurate?
(a) in both modgls cyclical solar activity is regarded as a long-lived
feature of the sun, persisting with little change over billions of years.
(b) tn both models the solar-activity cycle is hypothesized as being
dependent on the large-scale solar maic field.
(c) tn one model the sun’s maic fieid is thought to play a role in
causing solar activ- ity, whereas in the other model it is not.
(d) in one model solar activity is presumed to be unrelated to terrestrial
phenomena. whereas in the other model solar activity is thought to have
observable effects on the earth.
(e) in one model cycles of solar activity with peri- odicities longer than
a few decades are con- sidered to be impossible, whereas in the other model
such cycles are predicted.

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