Sometime after midnight on February 8,1969, a large, brightmeteorentered Earth'satmosphereand broke into thousands of pieces, plummeted to the ground, andscatteredover an area 50 miles long and 10 miles wide in thestateof Chihuahua in Mexico. The firstmeteoritefrom this fall was found in the village of Pueblito de Allende. Altogether,roughlytwo tons ofmeteoritefragments were recovered, all of whichbearthe name Allende for thelocationof the first discovery.

Individualspecimens of Allende are covered with a black, glassycrustthat formed when their exteriors melted as they were slowed by Earth'satmosphere. When broken open, Allende stones are revealed tocontainanassortmentof small,distinctiveobjects,sphericalorirregularinshapeand embedded in a dark gray matrix (bindingmaterial), which were once constituents of thesolarnebula—theinterstellarcloud of gas and dust out of which oursolarsystem was formed.

The Allendemeteoriteis classified as a chondrite. Chondrites take their name from the Greek word chondros—meaning "seed"—an allusion to theirappearanceas rocks containing tiny seeds. These seeds are actually chondrules: millimeter-sized melted droplets ofsilicatematerialthat were cooled into spheres of glass andcrystal. A few chondrulescontaingrains that survived themeltingevent, so these enigmatic chondrules must have formed whencompactmasses of nebular dust were fused at high temperatures—approaching 1,700 degrees Celsius—and then cooled before these surviving grains couldmelt. Study of the textures of chondrules confirms that they cooled rather quickly, in times measured in minutes or hours, so the heating events that formed them must have been localized. It seems veryunlikelythat large portions of thenebulawere heated to suchextremetemperatures, and hugenebulaareas could not possibly have lost heat so fast. Chondrules must have been melted in small pockets of thenebulathat were able to lose heat rapidly. Theoriginof thesepeculiarglassy spheres remains an enigma.

Equallyperplexingconstituents of Allende are the refractory inclusions:irregularwhite masses thattendto be larger than chondrules. They are composed of minerals uncommon on Earth, all rich incalcium,aluminum, and titanium, the most refractory (resistanttomelting) of themajorelements in thenebula. The same minerals thatoccurin refractory inclusions are believed to be the earliest-formed substances to have condensed out of thesolarnebula. However, studies of the textures of inclusionsrevealthat the order in which the minerals appeared in the inclusions varies frominclusiontoinclusion, and often does notmatchthetheoreticalcondensationsequencefor those metals.

Chondrules and inclusions in Allende are held together by the chondrite matrix, a mixture offine-grained, mostlysilicateminerals that also includes grains of iron metal and ironsulfide. At one time it was thought that these matrix grains might be pristine nebular dust, thesortofstufffrom which chondrules and inclusions were made. However, detailed studies of the chondrite matrix suggest that much of it, too, has been formed bycondensationormeltingin thenebula, althoughminuteamounts of survivinginterstellardust are mixed with the processed materials.

All thesediverseconstituents are aggregated together to form chondritic meteorites, like Allende, that have chemical compositions much like that of the Sun. Tocomparethe compositions of ameteoriteand the Sun, it is necessary that we use ratios of elements rather thansimplythe abundances of atoms. After all, the Sun has many more atoms of anyelement, say iron, than does ameteoritespecimen, but the ratios of iron tosiliconin the two kinds of matter might becomparable. The compositional similarity isstriking. Themajordifferenceis that Allende isdepletedin the mostvolatileelements, likehydrogen,carbon,oxygen,nitrogen, and the noble gases,relativeto the Sun. These are the elements thattendto form gasesevenat very low temperatures. We might think of chondrites as samples of distilled Sun, asortofsolarsludgefrom which only gases have been removed. Sincepracticallyall thesolarsystem'smassresides in the Sun, this similarity in chemistry means that chondrites haveaveragesolarsystemcomposition, except for the mostvolatileelements; they are truly lumps of nebular matter, probablysimilarincompositionto the matter from which planets were assembled.

Questions:
question_stem: The word "location" in the passage is closest in meaning to
choices: tag: A
text: sight

tag: B
text: sake

tag: C
text: success

tag: D
text: place
answer_key: D
explanation: D location: 位置。A 是景象，眼界；B 是目的，利益；C 是成功；D 是地点。所以正确答案是 D 的 place。

question_stem: Which of the following can be inferred from paragraph 1 about the large meteor that entered Earths atmosphere on February 8, 1969?
choices: tag: A
text: It was almost ten miles wide.

tag: B
text: It was the biggest meteor ever to hit Mexico.

tag: C
text: It weighed more than two tons.

tag: D
text: It broke into more pieces than most meteors do.
answer_key: C
explanation: C 没什么特别好的定位词，整一段都是在描述这块 meteor 的相关内容，但是这一段较短，可以快速通读。A 的 ten miles wide 出现在第一句，原句说的不是那个 meteor ten miles wide，是那个区域，所以 A 错；B 的 biggest 没说也没有相关信息可以推断，而且太绝对；C 正确，原文第二句说收集了大致两吨的碎片，碎片都有两吨了，那 meteor 自然不止两吨，所以 C 正确；D 的 more pieces 原文没有信息可以推断，不选。

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: Allende meteorites were formed when constituents of the interstellar cloud of gas and dust got trapped inside small, roughly spherical objects and these objects became bound together in a dark gray matrix.

tag: B
text: Inside Allende meteorites is a dark gray matrix that binds together small spherical or irregular objects formed from the interstellar cloud of gas and dust out of which the solar system was made.

tag: C
text: By breaking open Allende meteorites, scientists were able to find out what the solar nebula was made of.

tag: D
text: Allende meteorites were filled with material formed almost entirelyfrom interstellar gas and dust.
answer_key: B
explanation: B 这个句子看上去有点儿复杂，但把没用的部分去掉之后，剩下的东西并不多，只有 when blabla，A 包含各种各样的 objects，后面的一大堆东西都是修饰 objects 的，所以正确答案是 B。A 选项的 A form 原文没说，而且 cloud of gas and dust got trapped 原文也没说；C 和 D 的主干完全错误。

question_stem: The word "allusion" in the passage is closest in meaning to
choices: tag: A
text: addition

tag: B
text: modification

tag: C
text: resemblance

tag: D
text: reference
answer_key: D
explanation: D allusion: 暗指，暗示。A 是添加；B 是改变，修正；C 是相似；D 是指的是，参考。所以正确答案是 D 的 reference。

question_stem: The word "enigmatic" in the passage is closest in meaning to
choices: tag: A
text: dangerous

tag: B
text: mysterious

tag: C
text: interesting

tag: D
text: surprising
answer_key: B
explanation: B enigmatic: 神秘的，成谜的，来自 enigma 谜，所以正确答案是 B 的 mysterious（神秘的额）。A 是危险的；C 是有趣的；D 是令人惊讶的。

question_stem: According to paragraph 3, what does the presence of grains inside some of the chondrules indicate?
choices: tag: A
text: The chondrules were formed of silicate material.

tag: B
text: The chondrules were formed at high temperatures and then cooled rapidly.

tag: C
text: The grains were formed in huge areas of the solar nebula

tag: D
text: The grains were formed after the chondrules were fused together into chondrites.
answer_key: B
explanation: B 以 presence of grains inside some of the chondrules 做关键词定位至第四句，也就是刚才词汇题所在的那句，说 C 包含了 melting 之后剩下的颗粒，这些神奇的颗粒一定是在高温下 nebular dust were fused 的时候形成的，然后快速冷却，所以正确答案是 B。A 说的是对的，但问题问的是 grains indicate 什么，A 答非所问，不选；C 完全没说；D 的 after 错，不选，原文说的是 when，而且 fuse into 什么原文也没说。

question_stem: According to paragraph 4, all of the following are true about the minerals found in the refractory inclusions EXCEPT:
choices: tag: A
text: These minerals are among the most resistant to melting of all the major elements in the solar nebula.

tag: B
text: These minerals are believed to be some of the first elements to have condensed out of the solar nebula.

tag: C
text: These minerals are among the least commonly found elements on Earth.

tag: D
text: These elements occur in the order that scientists would have predicted.
answer_key: D
explanation: D EXCEPT 题，排除法。A 的 most resistant to melting 做关键词和 C 的 least commonly found 都定位至第二句，正确，都不选；B 的 first elements 做关键词定位至第三句，earliest- formed 与 first 同义替换，正确，不选；D 的 order 做关键词定位至最后一句，最后一句说 order varies from inclusion to inclusion，所以 scientist 不能预测，D 说反，选。

question_stem: The word "pristine" in the passage is closest in meaning to
choices: tag: A
text: pure

tag: B
text: solid

tag: C
text: ordinary

tag: D
text: trapped
answer_key: A
explanation: A pristine: 原始的，纯朴的。A 是纯的，纯洁的；B 是结实的，固体的；C 是正常的；D 是捕获的，收集的。所以正确答案是 pure。

question_stem: According to paragraph 5, which of the following is indicated by studies of the mixture holding the inclusions together?
choices: tag: A
text: Large amounts of this material were formed by condensation or melting in the nebula.

tag: B
text: This material contains more iron and iron sulfide than had previously been thought.

tag: C
text: This material is very similar to the material from which the refractory inclusions are made

tag: D
text: The grains in this material are made from the same elements as chondrules are.
answer_key: A
explanation: A  以 mixture holding the inclusions together 做关键词定位至最后一句，说 matrix 是 nebula 里面通过 condensation 和 melting 形成的，所以正确答案是 a。b 的比较没说，不选；c 完全没说；d 的 same material 没说，都不选

question_stem: In paragraph 6, why does the author mention that "the Sun has many more atoms of any element, say iron, than does a meteorite specimen"?
choices: tag: A
text: To show how difficult it is to compare the composition of a meteorite with that of the Sun

tag: B
text: To explain why a comparison of the compositions of a meteorite and of the Sun has to be done in terms of ratios of elements

tag: C
text: To identify the most common element in both the Sun and meteorite specimens

tag: D
text: To emphasize how much largerthe Sun is than any meteorite specimen is
answer_key: B
explanation: B 修辞目的题，先看例子所在句，但这句话整个是一个例子，所以看前一句。前句说为比较陨星和太阳的组分，应该应用的是元素的比值而不是单纯应用元素的丰度，所以正确答案是 b，c 和 d 完全不靠谱，a 的 difficult 原文没说，不选

question_stem: According to paragraph 6, the composition of chondritic meteorites differs from the composition of the Sun primarily in
choices: tag: A
text: containing nebular matter

tag: B
text: containing many fewer atoms of iron

tag: C
text: the relative amount of volatile elements

tag: D
text: the ratio of iron to silicon
answer_key: C
explanation: C 以 differ 做关键词定位至第五句，说最主要的区别在于与太阳相比，a 没有挥发性元素，所以正确答案是 c，其他答案都没说.

question_stem: According to paragraph 6, what is the significance of the similarity in composition between chondrites and the Sun?
choices: tag: A
text: It indicates what the matter from which planets were formed was probably like.

tag: B
text: It may explain howthe Sun originally developed.

tag: C
text: It helps scientists estimate the variations in the chemical composition of different meteors.

tag: D
text: It suggests that most meteorites may contain large quantities of volatile elements.
answer_key: A
explanation: A 以 similarity 做关键词定位至第四句和最后一句，但第四句什么都没讲，所以答案在最后一句，说除了 c 没有可挥发性元素之外，其他的成分都与太阳系的平均成分相同，是 nebular 的 lump，同行星组分相同，所以正确答案是 a。b 错，原文说的是行星形成，不是太阳；c 的 variation 没说；d 的有挥发性元素不是 similarity 体现的，不选