The surface of Mars shows a wide range of geologic features, including huge volcanoes-the largest known in thesolarsystem-andextensiveimpactcratering. Three very large volcanoes are found on the Tharsisbulge, anenormousgeologic area near Mars’sequator. Northwest of Tharsis is the largestvolcanoof all: Olympus Mons, with a height of 25 kilometers and measuring some 700 kilometers indiameterat its base. The three large volcanoes on the Tharsisbulgeare a little smaller-a “mere” 18 kilometers high.

None of these volcanoes was formed as a result of collisions between plates of the Martian crust-there is noplatemotionon Mars. Instead, they areshieldvolcanoes-volcanoes withbroad, sloping slides formed bymoltenrock. All four showdistinctivelavachannels and other flow featuressimilarto those found onshieldvolcanoes on Earth. Images of the Martian surfacerevealmany hundreds of volcanoes. Most of the largest volcanoes are associated with the Tharsisbulge, but many smaller ones are found in the northern plains

The great height of Martian volcanoes is a directconsequenceof theplanet’s low surfacegravity. Aslavaflows and spreads to form ashieldvolcano, thevolcano’s eventual height depends on the new mountain’sabilityto support its own weight. Thelowerthegravity, the lesser the weight and the greater the height of the mountain. It is noaccidentthat Maxwell Mons onVenusand the Hawaiianshieldvolcanoes on Earth rise to about the same height (about 10 kilometers) above theirrespectivebases-Earth andVenushavesimilarsurfacegravity. Mars’s surfacegravityis only 40 percent that of Earth, so volcanoes riseroughly2.5 times as high. Are the Martianshieldvolcanoes still active? Scientists have no directevidencefor recent orongoingeruptions, but if these volcanoes were active as recently as 100 million years ago (anestimateof the time of lasteruptionbased on theextentofimpactcratering on their slopes), some of them may still be atleastintermittentlyactive. Millions of years, though, may pass between eruptions.

Anotherprominentfeature of Mars’s surface is cratering. The Marinerspacecraftfound that the surface of Mars, as well as that of its two moons, is pitted withimpactcraters formed by meteoroids falling in fromspace. As on our Moon, the smaller craters are often filled with surface matter-mostly dust-confirming that Mars is a drydesertworld. However, Martian craters get filled inconsiderablyfaster than theirlunarcounterparts. On the Moon,ancientcraters less than 100 metersacross(corresponding to depths of about 20 meters) have been obliterated,primarilyby meteoriticerosion. On Mars, there arerelativelyfew craters less than 5 kilometers indiameter. The Martianatmosphereis anefficienterosive agent, with Martian winds transporting dust from place to place and erasing surface features much faster than meteoritic impacts alone can obliterate them.

As on the Moon, theextentof largeimpactcratering (i.e. craters too big to have been filled in byerosionsince they were formed) serves as an age indicator for the Martian surface. Age estimates ranging from four billion years for Mars’s southern highlands to a few hundred million years in the youngestvolcanicareas were obtained in this way.

The detailedappearanceof Martianimpactcraters provides an important piece of information about conditions just below theplanet’s surface.Martian craters are surrounded

byejecta(debrisformed as a result of animpact) that looks quite different from itslunarcounterparts.Acomparisonof the Copernicuscrateron the Moon with the (fairlytypical)craterYuty on Mars demonstrates the differences.Theejectasurrounding thelunarcrateris just what one wouldexpectfrom anexplosionejecting a largevolumeof dust, soil, and boulders.However, theejectaon Mars gives thedistinctimpressionof aliquidthat has splashed or flowed out ofcrater.Geologists think that this fluidizedejectacraterindicates that alayerof permafrost, or water ice, lies just a few meters under the surface.Explosive impacts heated and liquefied the ice, resulting in thefluidappearanceof theejecta. Martian craters are surrounded

byejecta(debrisformed as a result of animpact) that looks quite different from itslunarcounterparts. Acomparisonof the Copernicuscrateron the Moon with the (fairlytypical)craterYuty on Mars demonstrates the differences. Theejectasurrounding thelunarcrateris just what one wouldexpectfrom anexplosionejecting a largevolumeof dust, soil, and boulders. However, theejectaon Mars gives thedistinctimpressionof aliquidthat has splashed or flowed out ofcrater. Geologists think that this fluidizedejectacraterindicates that alayerof permafrost, or water ice, lies just a few meters under the surface. Explosive impacts heated and liquefied the ice, resulting in thefluidappearanceof theejecta.

Questions:
question_stem: The word “enormous” in the passage is closest in meaning to
choices: tag: A
text: Important

tag: B
text: Extremely large

tag: C
text: Highly unusual

tag: D
text: Active
answer_key: B
explanation: B enormous: 庞大的，巨大的。A 选项是重要的，B 选项是非常大的，C 选项是极其不寻常的，D 选项是活跃的。根据词意，B 选项正确。

question_stem: According to paragraph 1, Olympus Mons differs from volcanoes on the Tharsis bulge in that Olympus Mons
choices: tag: A
text: Has more complex geologic features

tag: B
text: Shows less impact cratering

tag: C
text: Is taller

tag: D
text: Was formed at a later time
answer_key: C
explanation: C 注意问的是 Olympus M，以这个词做关键词定位至第三句，讲 O 是最大的，所以正确答案只能是 C，比较高，如果不确定可以往下看到最后一句，说三个大的跟 O 比起来要小点儿，也说明 O 比较大，其他答案都没说

question_stem: The word “distinctive” in the passage is closest in meaning to
choices: tag: A
text: Deep

tag: B
text: Complex

tag: C
text: Characteristic

tag: D
text: Ancient
answer_key: C
explanation: C distinctive: 与众不同的，有特色的。A 选项是深的，B 选项是复杂的，C 选项是特有的，有特色的，D 选项是古老的。根据词意，C 选项正确。

question_stem: According to paragraphs 1 and 2, which of the following is NOT true of the shield volcanoes on the Tharsis bulge?
choices: tag: A
text: They have broad, sloping sides.

tag: B
text: They are smaller than the largest volcano on Mars.

tag: C
text: They have channels that resemble the lava channels of volcanoes on Earth.

tag: D
text: They are over 25 kilometers tall.
answer_key: D
explanation: D  信息题-逐一排除； A 定位第二段第二句话, 正确； B 定位第一段最后一句话，正确； C 定位第二段第三句话关键词“ similar to" D 明显错误，直接定位第一段最后一句话。” The three larfe volcanoes on the Tharsis bulge... a "mere" 18 kilometers high.

question_stem: The word “roughly” in the passage is closest in meaning to
choices: tag: A
text: Typically

tag: B
text: Frequently

tag: C
text: Actually

tag: D
text: Approximately
answer_key: D
explanation: D roughly: 概略地，粗略地。A 选项是典型地，B 选项是频繁地，C 选项是事实上地，D 选项是大约地。根据词意，D 是正确选项。

question_stem: In paragraph 3, why does the author compare Maxwell Mons on Venus to the Hawaiian shield volcanoes on Earth?
choices: tag: A
text: To help explain the relationship between surface gravity and volcano height

tag: B
text: To explain why Mars’s surface gravity is only 40 percent of Earth’s

tag: C
text: To point out differences between the surface gravity of Earth and the surface gravity of Venus

tag: D
text: To argue that there are more similarities than differences between volcanoes on different planets
answer_key: A
explanation: A 修辞目的题。找到逻辑上一层。题干的支持句支撑的是第三段的第三句。把第三句的关键词 “gravity" 和 "weight" &" height" 联系起来，即可找到正确选项：A

question_stem: 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.
choices: tag: A
text: Although direct evidence of recent eruptions is lacking, scientists believe that these volcanoes were active as recently as 100 million years ago.

tag: B
text: Scientists estimate that volcanoes active more recently than 100 years ago will still have extensive impact cratering on their slopes.

tag: C
text: If, as some evidence suggests, these volcanoes erupted as recently as 100 million years ago, they may continue to be intermittently active.

tag: D
text: Although these volcanoes were active as recently as 100 million years ago, there is no direct evidence of recent or ongoing eruptions.
answer_key: C
explanation: C 原句关键在于 But 后的句子，转折逻辑的重点都在转折之后，所以重点看 but 之后的内容。而 but 之后的主要逻辑是假设，抛去一些修饰成分，表达的主要意思是：如果这些火山100 million 年以前是活火山的话，那么他们现在应该也间歇性地活跃。C 选项将主干的这些要点都涵盖了，且转述正确，所以 C 为正确答案。A 选项将 if 引导的结论（still active）遗漏，所以错误；B 选项过度改写，后面的 extensive impact 根本没有提到过；D 选项将 if 引导的主干部分全部遗漏，所以错误。

question_stem: The word “considerably” in the passage is closest in meaning to
choices: tag: A
text: Frequently

tag: B
text: Significantly

tag: C
text: Clearly

tag: D
text: Surprisingly
answer_key: B
explanation: B considerably: 相当地，非常地。A 选项是频繁地，B 是显著地，C 是清晰地，D 是惊人地。根据词意，B 选项正确。

question_stem: According to paragraph 4, what is demonstrated by the fact that craters fill in much faster on Mars than on the Moon?
choices: tag: A
text: Erosion from meteoritic impacts takes place more quickly on Mars than on the Moon.

tag: B
text: There is more dust on Mars than on the Moon.

tag: C
text: The surface of Mars is a dry desert.

tag: D
text: Wind is a powerful eroding force on Mars.
answer_key: D
explanation: D 用题干关键词 caters fill in much faster 先进行定位，定位到 However 开始的那句话，这句话和其后面一句话都是细节性的描述，而这个事实想要 demostrate 的内容在该段最后一句话，那句话也有一个 faster：

question_stem: In paragraph 4, why does the author point out that Mars has few ancient craters that are less than 5 kilometers in diameter?
choices: tag: A
text: To explain why scientists believe that the surface matter filling Martian craters is mostly dust

tag: B
text: To explain why scientists believe that the impact craters on Mars were created by meteoroids

tag: C
text: To support the claim that the Martian atmosphere is an efficient erosive agent

tag: D
text: To argue that Mars experienced fewer ancient impacts than the Moon did
answer_key: C
explanation: C 跟 9 题是同一题，定位至倒数第二句后，发现整个句子是个例子，然后看前句，发现同样是个例子，然后看后一句，就是第 9 题的那句话就可以找到答案 C.

question_stem: According to paragraph 5, what have scientists been able to determine from studies of large impact cratering on Mars?
choices: tag: A
text: Some Martian volcanoes are much older than was once thought.

tag: B
text: The age of Mars’s surface can vary from area to area.

tag: C
text: Large impact craters are not reliable indicators of age in areas with high volcanic activity.

tag: D
text: Some areas of the Martian surface appear to be older than they actually are.
answer_key: B
explanation: B 题干关键词：科学家能从现象中得到什么？定位原文第五段第二句话：range from... Southern highlands... youngest volcanic areas.... 回到选项中：看到 vary from area to area. 选项 B。

question_stem: According to paragraph 6, the ejecta of Mars’s crater Yuty differs from the ejecta of the Moon’s Copernicus crater in that the ejecta of the Yuty crater
choices: tag: A
text: Has now become part of a permafrost layer

tag: B
text: Contains a large volume of dust, soil and boulders

tag: C
text: Suggests that liquid once came out of the surface at the crater site

tag: D
text: Was thrown a comparatively long distance from the center of the crater
answer_key: C
explanation: 题干关键词：找不同。回到原文，第六段四五句描述了月球和火星的不同。重点看 however 后面：a liquid that has splahed or flowed out of the crater. 再回到选项：很明显，C。