GRE考试

根据网考网考试中心的统计分析，以下试题在2019/9/10日GRE考试习题练习中，答错率较高，为：30%
【单选题】That large regions of the galaxy can be influenced by the formation of massive stars in a few localized regions requires that star formation somehow be coordinated over long periods of time. The process commences with a single O-type star or a cluster of such stars in a giant molecular cloud, around which stellar radiation, winds and explosions carve a modest cavity from of the surrounding interstellar medium, concomitantly destroying the progenitor clouD、Perchance this disturbance triggers star formation in a nearby cloud, and so on, until the interstellar medium in this corner of the galaxy resembles Swiss cheese, composed of what theorists have recently begun to refer to as bubbles, or superbubbles, one of the most exciting discoveries in astrophysics in years. Within a hot bubble, the sun has revealed itself in x-rays emitted by highly ionized trace ions such as oxygen and at some point in the process of its formation, nearby bubbles commence to overlap, coalescing into a superbubble. The energy from more and more O-type stars feeds this expanding superbubble until its natural buoyancy stretches it from the midplane up toward the halo, forming a chimney―the superbubble thus becomes a pathway for hot interior gas to spread into the upper reaches of the galactic atmosphere, producing a widespread coron
A、Far from its source of energy, the coronal gas slowly starts to cool and condense into clouds. Over eons, these clouds fall back to the galaxy’’s mid-plane, completing the fountain-like cycle and replenishing the galactic disk with cool clouds from which star formation begins anew. Star formation often occurs in sporadic but intense bursts, but in the Milky Way the competing feedback effects almost balance out, so that stars form at an unhurried pace―just 10 per year on average, except in some galaxies where positive feedback has gained the upper hanD、20 million to 50 million years ago, star formation in the central parts of M82 began running out of control. Our galaxy, too, may have had sporadic bursts, and the way these starbursts occur, and what turns them off must be tied to the complex relation between stars and the tenuous atmosphere from which they precipitate.　　Progress will be made in this complicated subject as astronomers continue to study how the medium is cycled through stars, through the different phases of the medium, and between the disk and the halo. Observations of other galaxies give astronomers a bird’’s-eye view of the interstellar goings-on, and answer such a critical question as whether stars are really the main source of power for the interstellar medium. The loop above theCassiopeia superbubble1looks uncomfortably similar to the prominences that arch above the surface of the sun, prominences which owe much to the magnetic field in the solar atmosphere, and scientists have begun to wonder if magnetic activity dominates our galaxy’’s atmosphere. Which of the following, if true, would most seriously undermine the validity of the model of star formation that is presented in the passage
A、
A、star is discovered that emits lower levels of trace ions than those discovered by x-rays of our galaxy’’s sun.
B．
A、section of the universe is discovered to lack both stars and any sort of interstellar medium.
C．
A、galaxy is discovered with a negative rate of star formation.
D．In one corner of the galaxy, coronal gas is discovered to rarify as it becomes cooler.
E．
A、superbubble is found of equal mass to the galaxy surrounding it.

网考网参考答案：D，答错率：30%
网考网试题解析：
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