本文是tpo42阅读答案解析：Callisto and Ganymede，希望可以对大家备考托福有更多资料参考，认真将这些考题分析一下，总结真题的重难点，对正式考试也会有帮助的。
paragraph 1
From 1996 to 1999, the Galileo spacecraft passed through the Jovian system, providing much information about Jupiter's satellites. Callisto, the outermost of Jupiter's four largest satellites, orbits the planet in seventeen days at a distance from Jupiter of two million kilometers. Like our own Moon. Callisto rotates in the same period as it revolves, so it always keeps the same face toward Jupiter. Its noontime surface temperature is only about -140°C, so water ice is stable on its surface year-round. Callisto has a diameter of 4.820 kilometers, almost the same as that of Mercury. Its mass is only one-third as great, which means its density must be only one-third as great as well. This tells us that Callisto has far less of the rocky metallic materials found in the inner planets and must instead be an icy body through much of its interior.
1. According to paragraph 1, which of the following statements about Callisto is true?
【事实信息题】
A. It is the satellite closest to Jupiter's surface
B. Its surface temperature is constant at all times of the day.
C. It has the same mass and diameter as the planet Mercury
D. It completes one rotation every seventeen days.
答案：D
解析：根据原文Callisto, the outermost of Jupiter's four largest satellites, orbits the planet in seventeen days at a distance from Jupiter of two million kilometers.可知，orbits the planet in seventeen days at a distance from Jupiter 对应D选项中的one rotation every seventeen days. 所以D选项正确。
2. According to paragraph 1, how do scientists know that Callisto is made up largely of ice?
【事实信息题】
A. A sample of its interior was taken by the Galileo spacecraft in the late 1990s
B. It has too low a density to contain much rocky metallic material
C. With a noontime surface temperature of only about .140° C. the ice on it never melts
D. All of the bodies in the Jovian system are icy, because they are so far from the Sun.
答案：B
解析：根据ice定位至原文This tells us that Callisto has far less of the rocky metallic materials found in the inner planets and must instead be an icy body through much of its interior. 其中far less of the rocky metallic materials对应B选项中的too low a density to contain much rocky metallic material. 所以B选项正确。
paragraph 2
Callisto has not fully differentiated, meaning separated into layers of different density materials. Astronomers can tell that it lacks a dense core from the details of its gravitational pull on the Galileo spacecraft during several very close flybys. This fact surprised scientists, who expected that all the big icy moons would be differentiated. It is much easier for an icy body to differentiate than for a rocky one, since the melting temperature of ice is so low. Only a little heating will soften the ice and get the process started, allowing the rock and metal to sink to the center and the slushy ice to float to the surface. Yet Callisto seems to have frozen solid before the process of differentiation was complete.
3.Why does the author provide the information that “It is much easier for an icy body to differentiate than for a rocky one”? 【事实信息题】
A. To support the claim that all of the big icy moons are differentiated
B. To suggest that Callisto may be a rocky body rather than an icy one
C. To explain why scientists expected Callisto to be differentiated
D. To refute the claim that Callisto could not differentiate because it was frozen solid
答案：C
解析：根据原文This fact surprised scientists, who expected that all the big icy moons would be differentiated.可知scientists expected对应C选项中的This fact surprised scientists. 所以C选项正确。
4. All of the following questions are answered in paragraph 2 EXCEPT: 【否定事实信息题】
A. Why was Callisto frozen solid before differentiation was complete?
B. What allows the process of differentiation to get started?
C. Why is it easier for an icy body to differentiate than a rocky one?
D. How do astronomers know that Callisto lacks a dense core?
答案：A
解析：原文Only a little heating will soften the ice and get the process started, allowing the rock and metal to sink to the center and the slushy ice to float to the surface.对应B选项。It is much easier for an icy body to differentiate than for a rocky one, since the melting temperature of ice is so low.对应C选项。Astronomers can tell that it lacks a dense core from the details of its gravitational pull on the Galileo spacecraft during several very close flybys. 对应D选项。所以选择A选项。
paragraph 3
Like our Moon's highlands, the surface of Callisto is covered with impact craters. The survival of these craters tells us that an icy object can form and retain impact craters m its surface. In thinking of ice so far from the Sun, it is important not to judge its behavior from that of the much warmer ice we know on Earth; at the temperatures of the outer solar system, ice on the surface is nearly as hard as rock, and behaves similarly. Ice on Callisto does not deform or flow like ice in glaciers on Earth. Callisto is unique among the planet-sized objects of the solar system in its absence of interior forces to drive geological evolution. The satellite was born dead and has remained geologically dead for more than four billion years.
5. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. 【句子简化题】
A. It should not be assumed that surface ice has the same characteristics wherever it is found
B. Surface ice and rock are much more similar in temperature in the outer solar system than they are on Earth.
C. The further away surface ice is from the Sun, the more its temperature differs from that of the warmer ice on Earth
D. In the cold of the outer solar system, surface ice is so hard it behaves more like rock than like the warmer ice on Earth
答案：D
解析：highlighted句子主干在后半部分，at the temperatures of the outer solar system, ice on the surface is nearly as hard as rock, and behaves similarly.注意之间的比较关系，参考前半句话，much warmer ice we know on Earth. 所以只有D选项符合句意。
6.According to paragraph 3, how is Callisto different from all other planet-sized objects in the solar system? 【事实信息题】
A. It can form and retain impact craters on its icy surface
B. It has ice glaciers that do not flow or deform.
C. It has never had the interior forces required for geological evolution.
D. It is more than four billion years old.
答案：C
解析：根据planet-sized objects 定位至原文its absence of interior forces to drive geological evolution可知，木卫星缺少内部动力来引发地质演化，其中its absence对应C选项的It has never had, 所以C选项正确。
本文是托福tpo42阅读答案解析：Callisto and Ganymede。
paragraph 4
Ganymede, another of Jupiter's satellites and the largest in our solar system, is also cratered, but less so than Callisto. About one-quarter of its surface seems to be as old and heavily cratered; the rest formed more recently, as we can tell by the sparse covering of impact craters as well as the relative freshness of the craters. Ganymede is a differentiated world, like the terrestrial planets. Measurements of its gravity field tell us that the rock and metal sank to form a core about the size of our Moon, with a mantle and crust of ice floating above it. In addition, the Galileo spacecraft discovered that Ganymede has a magnetic field, the signature of a partially molten interior. Ganymede is not a dead world, but rather a place of continuing geological activity powered by an internal heat source. Much of its surface may be as young as half a billion years.
7. The word “signature” in the passage is closest in meaning to 【词汇题】
A. primary cause
B. end result
C. identifying mark
D. by-product
答案：C
解析：signature, 签名，信号，标志。
Primary cause, 主因。End result, 最终结果。Identifying mark, 识别标记。By-product, 副产品。所以C选项正确。
8. According to paragraph 4, each of the following provides evidence about Ganymede's interior EXCEPT 【否定事实信息题】
A. Ganymede's large size
B. measurements of Ganymede's gravity field
C. the fact that Ganymede has a magnetic field
D. the fact that Ganymede continues to be geologically active
答案：A
解析：原文Measurements of its gravity field tell us that the rock and metal sank to form a core about the size of our Moon,对应B选项。the Galileo spacecraft discovered that Ganymede has a magnetic field, 对应C选项。but rather a place of continuing geological activity powered by an internal heat source, 对应D选项。所以选择A选项。
paragraph 5
The younger terrain is the result of tectonic and volcanic forces Some features formed when the crust cracked, flooding many of the craters with water from the interior. Extensive mountain ranges were formed from compression of the crust, forming long ridges with parallel valleys spaced one to two kilometers apart. In some places older impact craters were split and pulled apart. There are even indications of large-scale crustal movements that are similar to the plate tectonics of Earth.
9. The word “Extensive” in the passage is closet in meaning to 【词汇题】
A. Unusual
B. Large
C. New
D. Steep
答案：B
解析：extensive, 大量的，广阔的。
Unusual, 与众不同的。Large, 大的。New, 新的。Steep, 陡峭的。所以B选项正确。
10. Paragraph 5 supports each of the following statements about Ganymede EXCEPT:
【否定事实信息题】
A. All water on it has always been frozen solid.
B. There is evidence that part of its crust once broke open
C. Its crust has been subject to forces that have created mountains and valleys.
D. Some of its older craters have been split apart by more recent geological activity
答案：A
解析：原文Some features formed when the crust cracked对应B选项，其中crust cracked对应B选项中的crust once broke open.原文Extensive mountain ranges were formed from compression of the crust, forming long ridges with parallel valleys spaced one to two kilometers apart.对应C选项。原文In some places older impact craters were split and pulled apart.对应D选项。所以选择A选项。
paragraph 6
Why is Ganymede different from Callisto? Possibly the small difference in size and internal heating between the two led to this divergence in their evolution. But more likely the gravity of Jupiter is to blame for Ganymede's continuing geological activity. Ganymede is close enough to Jupiter that tidal forces from the giant planet may have episodically heated its interior and triggered major convulsions on its crust.
11. According to paragraph 6, the differences in how Callisto and Ganymede evoked are most probably due to differences in their 【事实信息题】
A. size and internal heating
B. distance from Jupiter
C. chemical and physical composition
D. age
答案：B
解析：根据原文Ganymede is close enough to Jupiter that tidal forces from the giant planet may have episodically heated its interior and triggered major convulsions on its crust.可知，Ganymede距离木星更近，其中Ganymede is close enough to Jupiter对应B选项的distance from Jupiter, 所以选项B正确。
12. Look at the four squares [■] that indicate where the following sentence could be added to the passage. 【句子插入题】
The difference between Ganymede and Callisto, however, extend much further below the surface of the satellites.
Where would the sentence best fit? Click on square [■] to add the sentence to the passage
Ganymede, another of Jupiter's satellites and the largest in our solar system, is also cratered, but less so than Callisto. [■] About one-quarter of its surface seems to be as old and heavily cratered; the rest formed more recently, as we can tell by the sparse covering of impact craters as well as the relative freshness of the craters. [■] Ganymede is a differentiated world, like the terrestrial planets. [■] Measurements of its gravity field tell us that the rock and metal sank to form a core about the size of our Moon, with a mantle and crust of ice floating above it. [■] In addition, the Galileo spacecraft discovered that Ganymede has a magnetic field, the signature of a partially molten interior. Ganymede is not a dead world, but rather a place of continuing geological activity powered by an internal heat source. Much of its surface may be as young as half a billion years.
答案：B
解析：待插入句子意为，Ganymede和Callisto的差别延伸到了卫星表面之下很远。B选项之后的内容就开始说Ganymede和Callisto的具体不同之处了。所以B选项正确。
13. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selected THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.【表格题】
Drag your choices to the spaces where they belong. To review the passage, click on View Text
Between 600 B.C. and 450 B.C., Athens changed the distribution of political power between the aristocracy and ordinary citizens.
Callisto
Ganymede
Answer Choices
A. It has a core that consists mainly of rock and metal.
B. It may have formed as recently as half a billion years ago
C. Its interior is not fully solid
D. Its evolution has probably been strongly influenced by Jupiter's gravity
E. It always keeps the same face toward Jupiter as it orbits the planet
F. Its crust is covered by slow-moving glaciers
G. Its entire surface is heavily cratered
答案：
Callisto：E, G
Ganymede：A, C, D
解析：
Callisto：
根据原文Callisto rotates in the same period as it revolves, so it always keeps the same face toward Jupiter.可知E选项正确。
根据原文Ganymede, another of Jupiter's satellites and the largest in our solar system, is also cratered, but less so than Callisto.其中is also cratered, but less so than Callisto对应G选项中的Its entire surface is heavily cratered. 所以G选项正确。
Ganymede：
根据原文Ganymede is a differentiated world, like the terrestrial planets. Measurements of its gravity field tell us that the rock and metal sank to form a core about the size of our Moon, with a mantle and crust of ice floating above it.其中the rock and metal sank to form a core对应A选项中的a core that consists mainly of rock and metal, 所以A选项正确。
根据原文In addition, the Galileo spacecraft discovered that Ganymede has a magnetic field, the signature of a partially molten interior.其中molten interior对应C选项中的not fully solid. 所以C选项正确。
根据原文But more likely the gravity of Jupiter is to blame for Ganymede's continuing geological activity.可知D选项正确，Ganymede的演变是被木星的地心引力所影响的。
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