GMAT阅读模拟试题考前练习9

>>GMAT模拟题练习：GMAT阅读模拟试题考前练习9

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Before the age of space exploration, astronomers assumed that the Moon's core was smaller than the Earth’s, in both relative and absolute terms – the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass – but they had no way to verify this. Two sets of data gathered by Lunar Prospector have now given astronomers the ability to determine that the Moon's core accounts for 20 percent of the Moon's radius and for a mere 2 percent of its overall mass.

First, scientists measured minute, relatively rapid variations in the wavelength of radio signals from Lunar Prospector as the craft moved towards or away from the Earth. Using these variations, scientists accurately determined even slight changes in the craft's velocity while the craft orbited the Moon, changes resulting from inconsistency in the gravitational pull of the Moon on the craft. The data were used to create a "gravity map" of both near and far sides of the Moon, highlighting new details of the distribution of the Moon's internal mass. Scientists thus determined that the Moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the Moon itself by the Moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.

The size and composition of the Moon's core have serious implications for our understanding of the Moon's origins. If the Moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the Moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps due to a major asteroid impact that could have loosened a chunk of iron, allowing it to form the core around which the Moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.

1、The author most likely mentioned "gravity map" in the second paragraph in order to

A.illustrate the method used to correct the Lunar Prospector's velocity

B.confirm the results obtained by examining the Moon's magnetic field

C.detail a step in the investigation of the composition of a specific orbiting body

D.detail a step in the investigation of the effects of gravity on the Moon and the Earth

E.explain a step in the process of confirming a new hypothesis and discarding an older theory

正确答案：C

GMAT阅读题目解析

定位处： The data were used to create a gravity map of both near and far sides of the Moon, highlighting new details of the distribution of the Moon's internal mass. 这些数据被用来创建月球近端和远端的重力图，突出了月球内部质量分布的新细节。|| 科学家可测量航天器无线电波长变化，根据波长变化可确定航天器速度变化，根据速度变化可确定月球引力变化;把引力绘制成图，就可确定月球质量分布。|| 感觉在选项里找不到答案时，一定回原文看划线所在句，上下句。凭记忆总会错。

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