题目信息
This passage is excerpted from material published
in 1997.
Is there a massive black hole at the center of our
galaxy, the Milky Way? The evidence is inconclusive.
Just as the Sun's mass can be determined, given
knowledge of other variables, by the velocity at
which its planets orbit, the mass at the center of the
Milky Way can be revealed by the velocities of stars
and gas orbiting the galactic center. This dynamical
evidence, based on recently confirmed assumptions
about the stars' velocities, argues for an extremely
compact object with a mass two to three million
times the mass of our Sun. Although according to
current theory this makes the mass at the center
of the galaxy too dense to be anything but a black
hole, the relative lack of energy radiating from the
galactic center presents a serious problem. A black
hole's gravity attracts surrounding matter, which
swirls around the black hole, emitting some energy
as it is engulfed. Scientists believe that the amount of
energy that escapes the black hole should be about
10 percent of the matter's rest energy (the energy
equivalent of its mass according to the equation
E=mc2). But when the energy coming from the
galactic center is compared towidely held predictions
based on how much matter should be falling into a
theoretical central black hole, there is a discrepancy
by a factor of a few thousand.
in 1997.
Is there a massive black hole at the center of our
galaxy, the Milky Way? The evidence is inconclusive.
Just as the Sun's mass can be determined, given
knowledge of other variables, by the velocity at
which its planets orbit, the mass at the center of the
Milky Way can be revealed by the velocities of stars
and gas orbiting the galactic center. This dynamical
evidence, based on recently confirmed assumptions
about the stars' velocities, argues for an extremely
compact object with a mass two to three million
times the mass of our Sun. Although according to
current theory this makes the mass at the center
of the galaxy too dense to be anything but a black
hole, the relative lack of energy radiating from the
galactic center presents a serious problem. A black
hole's gravity attracts surrounding matter, which
swirls around the black hole, emitting some energy
as it is engulfed. Scientists believe that the amount of
energy that escapes the black hole should be about
10 percent of the matter's rest energy (the energy
equivalent of its mass according to the equation
E=mc2). But when the energy coming from the
galactic center is compared to
based on how much matter should be falling into a
theoretical central black hole, there is a discrepancy
by a factor of a few thousand.
The primary purpose of the passage is to
A:present several theories that could account for a particular phenomenon
B:argue that a certain question needs to be reframed in light of new evidence
C:resolve an apparent inconsistency between two lines of evidence
D:explain why a certain issue remains unresolved
E:present evidence that calls into question certain assumptions of a current theory
参考答案及共享解析
共享解析来源为网络权威资源、GMAT高分考生等； 如有疑问，欢迎在评论区提问与讨论
本题耗时：
已选答案：
正确答案：
D:explain why a certain issue remains unresolved
答案 D
我们的目标是确定五个选项中哪一个最能表达文章的主要目的。这个问题是讨论文章主题的，以及这个主题是如何被讨论的:这篇文章主要关注的问题是关于银河系中心的质量。主要目的是解释为什么这个群体的具体性质没有得到充分的理解——至少在1997年当这篇文章被写出来的时候。
A.虽然这篇文章借鉴了一些理论发现，但并没有提出多种理论。
B.这篇文章暗示作者对银河系中心巨大的质量感到困惑，因为有证据表明相对较低水平的能量向外辐射。然而，这篇文章从未试图说服我们，这个问题需要重新定义。
C.这篇文章描述了两行证据之间明显的不一致，但并没有试图解决这种不一致。
D.正确。如上所述，这一选择表达了文章的主要目的;也就是说，为了解释为什么我们没有充分理解银河系中心质量的性质。
E.虽然提出的一些证据可能会对这篇文章撰写时流行的一个或多个理论假设提出质疑，但这篇文章本身并不主要关注于确定任何这样的假设。
我们的目标是确定五个选项中哪一个最能表达文章的主要目的。这个问题是讨论文章主题的，以及这个主题是如何被讨论的:这篇文章主要关注的问题是关于银河系中心的质量。主要目的是解释为什么这个群体的具体性质没有得到充分的理解——至少在1997年当这篇文章被写出来的时候。
A.虽然这篇文章借鉴了一些理论发现，但并没有提出多种理论。
B.这篇文章暗示作者对银河系中心巨大的质量感到困惑，因为有证据表明相对较低水平的能量向外辐射。然而，这篇文章从未试图说服我们，这个问题需要重新定义。
C.这篇文章描述了两行证据之间明显的不一致，但并没有试图解决这种不一致。
D.正确。如上所述，这一选择表达了文章的主要目的;也就是说，为了解释为什么我们没有充分理解银河系中心质量的性质。
E.虽然提出的一些证据可能会对这篇文章撰写时流行的一个或多个理论假设提出质疑，但这篇文章本身并不主要关注于确定任何这样的假设。
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